Whenever I turn on either a blue tooth pill-type speaker (Ultimate Ears) or blue tooth Bose headphones, Loopy freezes. Paid a lot of money for the speakers and phones and need them to work with my iPad Air. The Apple Store 'expert' couldn't help.
I tried my Plantronics Bluetooth headset and loopy occasionally froze, but when not frozen the sound came out of the iPad speaker. This also appears to be true for other music apps ( Guitarism). Bebot and ThumJam work with my headset.
Perhaps Apps have to be built to support Airplay. I think @Michael will have to comment on what is possible.
I've seen similar behaviour recently when I took Loopy out to my car to test it with its Bluetooth system (the only Bluetooth rig I have access to!). The problem is, Bluetooth's latency is HUGE - in my car, it's about a second round-trip. Loopy's buffers can't handle that much delay between input and output, so it behaves weirdly.
The thing is though, I could put in the time to fix that (instead of something else), but it'll still be totally unusable because of the latency problem - no one's gonna be able to sing a full second out of sync in order to record in sync
So: I highly recommend steering clear of Bluetooth for live looping. It just doesn't seem to be the right tool for the job, in my experience.