I have tiger barbs and rummys together in a tank, and they are doing fine together. My tiger barbs chase each other, but no one else. (I have 6 tiger barbs and 3 rummys, I know, not enough rummys to make a proper school, but it's all I could find in my area and I've never found them again) I have had them together for about three months, and no problems.
Forgot to mention, the tank is a 29 gallon.