gallos relationship with other mafioso in prison was very distant, probably due to all the trouble that he was causing on the outside with the columbo family. There was probably some element of protection from other wiseguys looking to kill him by surrounding himself with black gangsters, also he saw that the demographics were changing and that black gangsters were taking more control of criminal activities in their own communities. Also he still had plans to take over the family once he got out so making friends with barnes would only strengthen his side up, in fact there was an fbi informant who stated that gallo had sent some black hoods to intimidate joe colombo by having them follow and surveil him. Also i don't think he was a drug connect either just someone who helped barnes organise and get out of prison probably in exchange for his support.