I posted the question about SkyDemon muting on their forum but then got to thinking a bit more. Since SkyDemon has no connection nor input from my radio and there is no muting function in the iPad Bluetooth set up, it can only be my headset doing the muting. For once I read the manual and my headset (DC One-X) Bluetooth defaults to muting every time it is turned off. I had forgotten this, so much remember in future to press the Bluetooth button and disable muting each time, or else I rarely get the audio warnings because of radio transmissions, static or heavy breathing.
Sean has said he plugs his SkyDemon 3.5 mm audio lead into his headset control box to get SD's audio piped to his ears. I suspect there may well be muting on this circuit and, hopefully, a means of turning off that muting to get SD audio.