Every tank mate has the potential to get fight with the betta. I had bettas most of my life, and they aaaaalways had 2 african dwarf frogs in the tank with them.
Most of the frogs were great, a couple of them would play "let's chase each other" with the the betta (it was 2 ways, not just 1) and the one I have now gets along great with her. I got a 2nd, but she kept showing up with welts on her side. I thought my betta was picking on her, but I started catching the FROG antagonizing the betta. I had to get her a new home, and the lady who adopted the frog told me recently that she is so aggressive she also tries to attack the snails in the tank the lady put her in.
So african dwarf frogs are good... but any tank mate has the potential to not like the other tank mate. My husband's ghost shrimp also liked to bite/pinch his old betta, but the new betta chases him back and puts him in his place, hehe :)