Bettas are territorial and aggressive fish, period. Sometimes they work in a community and sometimes they don't. I'm guessing now that it's settled into the tank, it's claimed territory and is doing what bettas do.... If he is only shooing off the cats, it might be okay to leave him in there. If he is not actively going after them- he may just be protecting his new territory. Although, this could be stressful for the cats always having to run away. And also stressful for the betta as he is constantly having to protect his space. Bettas can be finniky to have in a community. I would leave everything alone for a few more days and see if the shooing off becomes more aggressive- if it does I would remove him. Or, you could try re-arranging your tank and providing lots of hiding spots for everybody and seeing if that helps out.
Platys, Tetras, Mollies, Bettas, BN Plecos
Red Eared Slider