I have two male betta's in two seperate tank. One, the older betta male is in my 260L community tank. Together with 24 rummy-nosed tetras, 11 corydoras sterbai, 6 Carnegiella strigata (don't know the english name), LDA-033 and some apple-snails. I've never had much trouble. Daniel (that's his name) his personality is quite relaxed and he really doesn't mind the tetra's. Sometimes they clash a little but he always bites them off if they try to nip his fins

. He also has enough hiding space between the wood, large plants and floating plants. I do think it's important if you do keep a betta in a community tank to have a larger tank and have enough space for both parties to get away from each other if they want to.
My other betta is located in my 60L tank with 4 pseudogastromyzon cheni, and there's never anything wrong there, he's the king of the tank. Swimming around and showing off his beautiful fins.
In the end my experience is that betta's tend to do a lot better in larger tanks then small tanks,with enough room and hiding spots.. I've also worked in a few pet shops on the aquarium departments. And betta's tend to look quite down in show-tanks. Because of either over-crowded tanks, too small tanks etc. There are always fish (especially small tetra's) who might like to nip at Betta's fins, but it also really depends per group and per fish, as it also depends per betta what personality they have if they attack other fish. So putting Betta's in a small tank is animal cruelty, give them space!