If you were to put a betta with a different breed of fish, I'd suggest monitoring the fish BEFORE you put the betta in. Try to see once the betta's in, if the fish act differently. Keep a close eye on the fish in the tank, including the betta for about a week or two. Keep monitoring after that. If all is well, the it's about clear you're betta has a more docile demeanor. Though anything could happen, and something could go terribly wrong. It's all a matter of risk.