I have two ottos with my african cichlids which are very agressive and
they seem to just ignore them. probably cause most of the time they
are stuck to the wall or laying on the gravel, so probably just blend
in with the rest of the soroundings. i have also had my ottos with a
weather loach and they got along fine. i would be cautious about
putting anything with a betta. i have tested some fish with bettas and
it seems like compatablilty is totally up to the personality of the
betta. mine in particular was very aggressive twards anything that was
yellow, orange or red. but i have had success with putting bettas with
my bottom feeding spotted rapheal. i don't even think that the betta
knew it was a fish. he actually layed right on top of him. niether
seemed to bother. well i hope my experience will help you.