That passage is there to allow metered air to ENTER the crankcase (through maf into throttle body through the hose into the valve cover/crankcase) when vacuum is pulling on the crankcase through the pcv. If you block it off without doing anything else, the same crankcase pressure that is now pushing oil through it is gonna push the oil out the next weakest link - rear main or front main seals, or gaskets === oil leaks. If you simply add a breather, then you allow unmetered air to enter the engine whenever the manifold is seeing vacuum.
The proper solution is to solve why the oil is getting in there in the first place -- not to simply block it off. If your pcv system is operating properly, and the baffle is in your valve cover oil filler neck, you shouldn't have oil being pushed into the throttle body with crankcase pressure.
The wild card here is that you have an engine that is producing so much blow-by (because it's 'tired' or seeing lots of boost/nitrous) that the stock pcv system can't vent the crankcase. If that's the case -- then you need more crankcase ventilation capacity.