I'm with Lilo here, plus an additional point:
Vito certainly had to know both Sol and Mac were dead. But he probably didn't know that Michael did it. He'd have figured that Sonny, the hothead, arranged both murders. I'm guessing that Vito figured (to himself) that if he hadn't been so badly wounded and were able to be in charge, he'd have figured a way to exact revenge on Tat and Sol without killing Mac--thereby avoiding the police crackdown that turned the other families against the Corleones. But he never dreamed it'd be Michael.

Should he have? Quite a few people here put the beginning of Michael's turn toward the Mafia to the hospital scene when he says, "I'm with you now, Pop." Those of us who believe that think that Michael meant "with you" as in "I'm through keeping the Family at arms-length--I'me with you." Vito, in his drugged state, probably thought he meant that he was physically with Vito--nothing more.

Danito, your post raises a subtle point:
Tom treats the killingof McCluskey in an offhand, matter-of-fact way: "Since the killing of McCluskey..." But he bears down on It was Michael who killed Sollozzo." Well, Michael killed both of them. Was the killing of Sollozzo more important or significant than the killing of McCluskey? He should have said, "Michael killed both of them."