Good question, Oli.

I think that Clemenza proved his loyalty to Michael, and after the move to Nevada, he kept Clem on a long leash. Maybe Clem mentioned something about the Rosatos--perhaps some job they did for him that he said he would reward them for. But, I can't see Clemenza directly involving Michael in the details of what would be, for Michael, a minor operational matter occurring far away in NY.

I think Roth pushed the Rosato affair on Michael for his own purpose--to deliberately stir conflict between Michael and Frankie, and to make his allies (Rosatos) stronger in NY. I posted a long time ago that Michael should have been suspicious of Roth pressing the Rosatos' claims. But I think Michael's greed for Roth's Havana holdings dulled his suspicions. And, if he did question Roth, ol' Hyman might have fixed him with the gimlet eye and said, "Michael, they helped me once and I owe them a favor. Do yourself a favor and go along--it'll be good for our deal."