The key requirement you’ve included suggests the service rep must perform these tasks in Airtable.
This is accomplished by merging the restricted data (in Google Cloud Platform) with the unrestricted data in Airtable into a single view that is in Airtable. If the restricted data is stored in Airtable, it violates the HIPAA premise, so the best you can do is make it look like the data is in Airtable.
You could build an extension that renders a combination of Airtable fields and Google Cloud Platform based data in a web UI. The web UI (of course) would need to be served from a HIPAA-compliant infrastructure (i.e., a secure Firebase hosting app).
This is a lot of engineering just to combine a few fields.
Appsheet is a fine tool and it certainly simplifies the HIPAA requirement. However, it is no Airtable. Perhaps you should look at SmartSuite.