Actually, thinking about mounting a Go-Pro, I think the things that would worry me more than disturbing airflow (unless it mounted somewhere totally dumb) would be:
a) that it fell off
b) that it fell off and struck the tail or somewhere else as it went or
c) that it detached from the mount and was retained by a strap and banged against the aircraft
d) that it mounted in a way that damaged the aircraft (ie self tapping screws into aircraft skin)
Also, you'd have some concern about embrittlement of the plastic case that might cause it to fail. And GoPro don't use self locking screws on any of the attachments, which might also allow the camera to fall.
These are probably reasons to make it easy for someone (eg a LAME) to fit one properly rather than forcing it all "underground" through overly arduous and clumsy regulation.