Plugging the Crank Vent will introduce high pressures inside the engine and oil will start to puke out of every orifice (ie, Dipstick, past the rings, valve cover, and any other old seal in your engine)
I highly recommend taking that little red cap off, and at least venting it to atmosphere.
Relax, it's just there so junk won't get down in there before I get the breather hose. It's on order.