Hi. I make a short message here and hope that the garmin crow reads this. I refer to their sticky message in this forum.
I know that there is a lots of different Android phones, and now quite a lot that supports bluetooth ble. Why not try to make it to works with the phones with vanilla android and that almost all the time runs the latest version of android, the Nexus devices. It it works with those phones, then it will work with the Android OS, and if some phones then dosent work, then it is the device manufacturer that made something that breaks the functionality.
So i think you should develop for the nexus devices and pure android and then if the manufacturer wants it to work then it is only to follow the android guidelines.