My Betta lives with a school of Ember tetras and amano shrimp. He leaves the amanos alone and just occasionally chases the tetras if they are too close. Nothing serious has happened, but depends on the betta.
I house my Betta with a group of 5 White Cloud Minnows in a 10g tank. His personality isn't very predatory so he ignores them for the most part. My WC Minnows love the current my filter produces and show no interest in the Betta. On occasion he will chase them if they get too close. I have some floating plants and some Wysteria to give the fish something to hide in.