Honestly, I had a basic what was called atlantic pygmy, by the LFS and it never bothered the couple damsels that were there since cycling the tank. It actually would eat nothing but fiddlers once it realized it could get away with it!
The problem with keeping fish and octopus together is that typically, the fish will actually bother the octopus too much, resulting in a pecked cephalopod.
Now and again, in a large enough tank, it can work out...especially with the dwarf species.
Note to members: let's keep the discussion civil, please.
I think I may be a special case but I have an 0.Briareus in a 125 gallon tank that lives with a blue tang, a yellow tang, a mimic tang, a mated pair of clown fish, 2 chromis, a checkered puffer, a flame hawk, a rock beauty angel, and two anemones. after a few months so far only one casualties, a gobie tried to steal her den and she took care of him, other than that everyone leaves the octo alone. However. from what I have read it usually doesn't work out that well. the difference may be that I raised my octo from a VERY young age, I caught her when she was only days old, just a clear blob with blue eyes.
I've kept 2 Abdopus aculeatus in 2 different community tanks, without any problems. They were mature when I got them, were not raised with the fish they were kept with.
My briareus ate a blue chromis within 12 hours of it entering the tank. It was a baby when I got it, but it wasn't raised with fish, and it had quite the attitude.
So many factors are going to play into whether it works out or not.
Can the tank handle the overall bioload?
Do these species interact in nature?
Do these species prey/predate upon each other in nature?
Is the tank big enough they can all hang out without annoying each other?
Some creatures aren't meant to co-exist in a glass box.