I think it were two separate situations. Both the Rosato brothers and Roth wanted others to believe that Michael ordered the death of Pentangeli.

The difference is that Roth didn't want Pentangeli to die, which is what the Rosato's intented.

That's why Roth probably informed the cops about what was going to happen, in the hope his plan would turn out like he intented, which it did.

I think at least the cop who walked in was on Roth's payroll.

The Rosato's were used by Roth. He enigneered the whole situation.