It doesn't really matter if the PV is open at idle since very little fuel is going to flow thru the PVCR channel at idle. If the PV is torn then the fuel will leak in the intake and that will cause a problem.

You can block off the PV's just to eliminate a variable, but an open PV shouldn't cause a rough idle.

If the vacuum is really low due to the new cam then the problem usually is getting enough air into the engine. The throttle shafts need to be in the correct location. If the engine needs more air at idle then you need to provide idle bypass air. You do not open up the throttle since that messes up the location of the throttle blades.

Dominators are easy to provide idle bypass air. You can drill and tap holes on the top of the carb that will let air into the manifold via some small jets.