But if an aviation ULB can't be distinguished from a similar device attached to an animal, you're depending on the aircraft crashing in an area where there aren't likely to be any tagged animals?
But they can be distinguished - aviation ULBs aren't coded, and transmit in bursts at 1 second intervals, not continuously. They also transmit around one frequency and will only have a doppler shift related to the velocity of the locator. If you've detected the signal over any substantial period of time I don't think it's going to be at all difficult to tell it apart from a marine animal tag.