well, I have corys in my betta tank, the most he has done so far, in his poke them a little bit. No biting, no hurting, nothin. Granted the cory's have alot of hiding places around driftwood and plants, but, ALSO, I have oto's in that same tank, and the betta is more interesting in zooming around the tank.
Betta's, from what I have seen, only get PO'ed at those that are the same size or bigger then they are, or have longer fins. ANd if u give the betta's enough to explore, they will be more entertained with that