Clemenza's loyalty to Mike when Mike and the family appeared to be weak (in GF I when Tessio turned on him) tells me that he would not have betrayed Mike over some squabble with the Rosato brothers. If you remember in GFII Mike tells Frankie that Clemenza promised territories to the Rosatos and that after he died Frankie welched, because, among other things he disapproved of their hiring practices. This shows Clemenza was towing the party line.