IMHO the task you imagine (supporting ALL hearing aid types) is simply impossible! T-Coil is the only technology that has any chance of being compatible across brands, but many audioligists and manufacturers manage to screw it up so that the person with the hearing aids has no idea how to use it.
You’ve probably already figured this out, but you need to be _very careful when the term “Bluetooth” (perhaps even with a version number) is used in the Hearing Aid context. Often this only means the PHY layer of standard Bluetooth is being used, but the profile is proprietary (controlled by Apple in the case of Made-For-iPhone). The only 100% standard Bluetooth solutions that are available have excessive latency (200ms or more) and so aren’t very well suited to applications where the voice needs to match the mouth (for example TV watching) and also require more power than Hearing Aid battery life expectations can deal with. The newer Bluetooth-Low-Energy (BLE) solves the power problem, but there is no standard profile that supports both audio streaming and control. (Until recently, and perhaps still, there was NO standard BLE profile that could carry streaming audio.)
Further, most Hearing Aid manufacturers conflate communication source<->medallion with communication medallion<->HearingAid. So when they say “Bluetooth”, they probably don’t mean that the Hearing Aids can do Bluetooth directly. What they mean is that the source<->medallion communication is standard Bluetooth, but the medallion<->HearingAid communication is actually something else (most likely Bluetooth-LIKE, which just adds even more to the confusion.)
While everybody says “Bluetooth”, very few hearing aids actually support a 100%-standard Bluetooth solution all the way to the Hearing Aids themselves. And it’s not at all clear that those that do are on the right track with a technology that will persist for more than just a couple of years.
Again in my opinion: it’s very sad that, due mainly to the behavior of the hearing aid manufacturers, it’s simply impossible -even for a supertech familiar with all the specs- to equip a building with any broadcast hearing aid system that will work for most of the hearing aids that come into the building.