Though he bitches about the Rosatos that "...an' everything with them is a babania...an' they leave the gambling for last," I think he's complaining about the emphasis they put on drugs and their neglect of the gambling business. He's not complaining that they deal drugs at all.
We see this again in GF III where Michael confronts Zasa about whether or not he guarantees that his people are not selling drugs in the old Italian neighborhoods. Zasa dodges the question by saying he makes no such guarantee, but that he would kill anyone he caught doing it.
