Why do so many people use... (A strange dream spoilers)

The music from the secret ending of ASD? None of the other music is allowed, but I see this used a lot, and no one ever complains about it. Is it allowed to use it?

The track used for ASD's secret ending is very similar to a default ambiance track (22). (It really is very, very similar, but crucially, it's not identical.) I've never seen the actual ASD track used in any other levels, but I've seen default ambiance 22 used plenty of times.

You've probably just mistaken 22 for the ASD custom track. (Which is incidentally also named Ambi22.)

Thanks! I didn't bother to check ambiance.
EDIT: I just compared them and they are noticeably different.