It's a totally unpredictable situation I'm afraid. It's completely dependent on the individual Betta's disposition, and you won't know untill you try. If you choose to do so, I'd start out with Ghost Shrimps for the obvious reason, lol. They'd likely have the best chance at living alongside a Betta as opposed to a Cherry or Crystal Red etc. considering they can blend in better with their environment. I would definitely recommend a heavily planted environment. Not only would it serve as added protection for them, it would provide a stimulating environment for them and their Betta tankmate. Out of all the Bettas I've had, only one got along famously with my Ghosties.