My betta isn't named Oscar the Grouch for no reason... He's grumpy, but not super aggressive. He chases the tetras from time to time, when they get too close, but he hasn't nipped one. And he tries to chase the cories, but they're just oblivious.
From what I've read, bettas will do better NOT being with longer/flowing finned fish. And conversely, fin nipping fish will looove the pretty betta fins.