I currently have a HM05 eBay Bluetooth adaptor that I use for wireless connection to my FT-817. I was planing on using these for my own Android projects, but at this stage I have not done so. I believe that it should be a simple serial connection. The Bluetooth device needs me to set up the serial speed on the hardware before connecting to the radio, so there is nothing that the app needs to do other than ask for a serial speed. This does mean that: FT817, HM05 & the phone need to have the same serial parameters to work correctly. I also have connection issues frequently that require me to power cycle (disconnect, reconnect) the device to connect correctly; this is probably an issue with low quality firmware.
I was also thinking about sometime in the future trying out a BLE device as well, but I have no idea if Android abstracts Bluetooth serial so that the app doesn’t need to know what type of device it is connecting to.