I'm not so sure we can be certain that Vito discussed the Carlo problem with Michael. Vito knew that Michael knew what a thread Carlo was.
On the other hand: Michael had put Carlo a little too close. Carlo should have smelled the rat when he heard he was going to be Michael's right hand man in Vegas, while Hagen was out. Carlo's little modest vain nod when he hears about his promotion is unforgettable.