If the crank case isn't ventilated and the PCV is the only exit path for pressure, then yes...if you block the last remaining exit path, the blow-by will pressurize the crank case to the point where it'll blow
oil past the front and rear seals. If that's not a good enough vent, it will blow out the end gaskets on the intake next usually. Not the best thing to try.
Big stroker engines, high compression, or anything else that increases blow-by more than what a normal production engine sees needs a bigger ventilation system. If you want to run a PCV system, then you probably need more than one PCV valve to make a large enough exit path. And even then, keep in mind that your engine is sucking crankcase vapor containing
oil...with is a very low octane fuel and induces detonation. Personally, I say forget the PCV and run an open crankcase unless the PCV is required. If you want crankcase vacuum, use a vacuum pump or a header evac system.