Michael needed Tom as his legitimate front man in Nevada like who doesn't remember him from the old days!
Johnny Ola remembered Tom from the old days--but not the Nevada Gaming Commissioners, and not the local and state politicians whom Michael needed to help establish his "legitimate" front. A good part of Tom's value to Vito was that he was accepted by the largely Irish and Jewish judges and politicians in NYC because he was a) a lawyer, not a gangster; b) not Italian; and c) never associated with the muscle end of the family. Those same virtues would make Tom effective with the largely Mormon politicos who controlled Nevada.
