I think Vito would have been very proud of Mike. At the beginning of III,he gets the Church Knighthood. As the story progresses,we learn more about Mike divesting the Family of all illegitimate business,and also the legal (and lucrative) Casino operations. The Vito Andolini Foundation and the role of Mary in administering it would have certainly touched Vito. And seeing Mike poised to become one of the richest legitimate businessmen in the world through the Immobilare deal would have been icing on the cake. Don't forget,in his heyday,Vito's "legitimacy" was very self-delusional. As we see in the headlines,both when Vito gets shot,and when he comes home from the hospital,the outside world knows full well who Vito Corleone really is. He is referred to as a "gambling boss,gang leader,and syndicate bigshot"