Healthcare companies following a schema? Ha. Maybe the closest thing to there being any consistency is companies making sure they can be listed in Apple's Health app.
The closest thing is probably companies assuring they can interact with the transaction formats mandated for electronic transactions under the HIPAA transactions and code sets rule, or EHR standards also mandated/incentivized by the federal government.
Most EHRs and other related healthcare applications now have reasonably correct support of various HL7 interoperability formats. Not perfect, but good enough. Much of this has been driven by federal government regulatory mandates.