You never know with a Betta. Some make great community fish, others not.
If you really want to test his temperment, it is okay to put him in the community tank and see how he does. Just do it at a time when you can watch his temperment (and the barbs too, they can be tempermental). If he doesn't try to fight or nip at the other fish, you know he's probably okay with other fish. Just avoid fish with longer fins, like leopard danios or longfin varieties of tetras. Bettas sometimes mistake them for other Bettas and the battles are visious and can end in death.