Successful hybrids with balls have been made for:
Burms
Retics
Angolans
Bloods/STPs
Carpets
Carpondros
Womas
I know it has been tried with straight GTP but that breeder did not have success. Given the success with carpets and carpondros I have no doubt it is possible though. And I have heard rumour of ball x AfRock and ball x BHP but never seen any actual proof on them