The uncertified ADS-B OUT devices (SIL=0/1) have no access to barometric altitude, AFAIK.
SIL level merely indicates the probability of position error. SIL=0 means ‘unknown’. SIL=3 means 1 in 10e-7. Nothing more, nothing less, it does not indicate whether or not a barometric sensor is present.
From AC 20-165
“(3) Source Integrity Level (SIL). SIL is typically a static (unchanging) value and may be set at the time of installation if a single type of position source is integrated with the ADS-B system. SIL is based solely on the position source’s probability of exceeding the reported integrity value and should be set based on design data from the position source equipment manufacturer. Installations which derive SIL from GNSS position sources compliant with any revision of TSO-C129, TSO-C145, TSO-C146, or TSO-C196 which output horizontal protection level (HPL) or horizontal integrity level (HIL) should set the SIL = 3 because HPL and HIL are based on a probability of 1×10-7 per hour. Do not base NIC or SIL on horizontal uncertainty level (HUL) information. "
Vertical isn’t even mentioned. If you read e.g. TSO-C145, the only mention of barometric is " If the equipment uses barometric-aiding to enhance the availability of FDE, it must meet the requirements in Appendix G of RTCA/DO-229C. ", the word ‘if’ makes it clear that a barometric source might not be used, it’s just one way of meeting the TSO. Also that’s fault detection and exclusion (FDE) and it’s not about transmitting baro information as part of the ADS-B packet. You can’t read anything into the SIL level of whether barometric information is present.
I agree, but that isn’t the point I was making 
Criteria for displaying ADS-B In targets on a CDTI does not allow display of targets with SIL=0. So SIL of 1, 2, or 3 would display. Surveillance is an ATC function, it requires a SIL of 3 for the ADS-B data to be used by a controller. SIL is only one parameter that is used by ATC in order to determine the usability of the ADS-B data by ATC.
From the Federal Register:
In deploying the ADS–B surveillance infrastructure, the FAA implemented a capability to monitor compliance with § 91.227 requirements for aircraft operating within the U.S. National Airspace System (NAS). Over the past three years, this monitoring has identified some ADS–B Out aircraft with non-performing equipment (NPE) transmitting data used by ATC and ADS–B-In-equipped aircraft that present a potential safety hazard to NAS operations, including but not limited to:Unassigned/invalid 24-bit ICAO addresses; incorrect flight identification codes; erroneous position reports; improper avionics integrity and accuracy levels; and missing data required by applicable regulations.
In 2016, the FAA started to remove incentives for non compliant ADS-B Out systems to receive TISB client services. Here is a part of their rational. NPE aircraft would also not get ADS-B surveillance services based on ADS-B and would revert to primary radar or secondary radar.
The aviation community has realized that uncertified ADS-B devices that broadcast ADS-B Out with NACp/NACv/SDA=01 will receive the FAA TIS-B/ADS-R services (aka, “activate TIS-B/ADS-R client status”), and evidence exists that over 500 aircraft are doing so. However, broadcasting ADS-B with NACp/NACv/SDA=0 has certain negative effects as described below. Note that aircraft broadcasting ADS-B Out with NACp/NACv/SDA=0 will not comply with 14 CFR 91.225 and 14 CFR 91.227 (the ADS-B Out rule) and cannot receive ATC separation services using ADS-B as the surveillance source.
Safety Concern: Per DO-317A (TSO-C195a), any ADS-B emitter broadcasting SDA=0, NACv=0 or NACp<5 will not be displayed on a TSO-compliant ADS-B-In system. In alignment with the requirements of FAA TSO-C199 and for the purpose of this document only, an ADS-B emitter with SDA=0, SIL2=0, NIC<5, NACv=0 or NACp<5 is defined as a non-performing emitter (NPE). Based on FAA monitoring data, it appears that 15% to 40% of the aircraft equipped with ADS-B V2 are broadcasting as NPEs to activate TIS-B/ADS-R client status for themselves, but in doing so are not displayed on TSO-compliant ADS-B-In systems. This introduces a potential safety hazard into the NAS. Presumably these NPE aircraft have a transponder, so they are seen by ATC and surrounding aircraft equipped with TCAS/TAS, but they are “unseen” by surrounding TSO-compliant ADS-B-In aircraft that do not have TCAS/TAS equipage.
TIS-B/ADS-R Client Status logic will be modified to only provide TIS-B/ADS-R client status to aircraft broadcasting ADS-B with NACp>4, NACv>0, SDA>0, SIL>0, and NIC>4. These criteria are aligned with the requirements of TSO-C199 and should remove the incentives for NPE use.
FAR 91.227 requires the following to operate in the mandate airspace, SIL is not the whole story!:
(i) The aircraft’s NACP must be less than 0.05 nautical miles; (NACp > 7)
(ii) The aircraft’s NACV must be less than 10 meters per second; (NACv >0)
(iii) The aircraft’s NIC must be less than 0.2 nautical miles; (NIC > 6)
(iv) The aircraft’s SDA must be 2; and
(v) The aircraft’s SIL must be 3.
(2) Changes in NACP, NACV, SDA, and SIL must be broadcast within 10 seconds.
(3) Changes in NIC must be broadcast within 12 seconds.
(d) Minimum Broadcast Message Element Set for ADS-B Out. Each aircraft must broadcast the following information, as defined in TSO-C166b or TSO-C154c. The pilot must enter information for message elements listed in paragraphs (d)(7) through (d)(10) of this section during the appropriate phase of flight.
(1) The length and width of the aircraft;
(2) An indication of the aircraft’s latitude and longitude;
(3) An indication of the aircraft’s barometric pressure altitude;
(4) An indication of the aircraft’s velocity;
(5) An indication if TCAS II or ACAS is installed and operating in a mode that can generate resolution advisory alerts;
(6) If an operable TCAS II or ACAS is installed, an indication if a resolution advisory is in effect;
(7) An indication of the Mode 3/A transponder code specified by ATC;
(8) An indication of the aircraft’s call sign that is submitted on the flight plan, or the aircraft’s registration number, except when the pilot has not filed a flight plan, has not requested ATC services, and is using a TSO-C154c self-assigned temporary 24-bit address;
(9) An indication if the flightcrew has identified an emergency, radio communication failure, or unlawful interference;
(10) An indication of the aircraft’s “IDENT” to ATC;
(11) An indication of the aircraft assigned ICAO 24-bit address, except when the pilot has not filed a flight plan, has not requested ATC services, and is using a TSO-C154c self-assigned temporary 24-bit address;
(12) An indication of the aircraft’s emitter category;
(13) An indication of whether an ADS-B In capability is installed;
(14) An indication of the aircraft’s geometric altitude;
(15) An indication of the Navigation Accuracy Category for Position (NACP);
(16) An indication of the Navigation Accuracy Category for Velocity (NACV);
(17) An indication of the Navigation Integrity Category (NIC);
(18) An indication of the System Design Assurance (SDA); and
(19) An indication of the Source Integrity Level (SIL).
(e) ADS-B Latency Requirements—
