The tiger barbs may find your betta's long flowy fins good to nip at. My very first tank I had was stocked with tiger barbs and they were nippers. You can always give it a try though, this is just my experience with them. They may leave the betta alone completely.
yeah I was going to get some tiger barbs but went against it after I did some research on them and found out they love to nip fins. It was lucky I did probably would have torn apart some of my more elagent fish