PCV stands for Positive Crankcase Ventilation.
Engine vacuum sucks air/vapor out of the crankcase.
It doesn't matter how air gets in, as long as it does...otherwise, you'll pull enough crankcase vacuum to pull
oil away from the seals and cause them to wear quickly.
If you've got the crankcase hooked to engine vacuum through a check valve and still see vapor out of the breather, you simply have more crankcase vapor being generated (blowby) than the PCV system is able to evacuate. Excessive blowby, or low engine vacuum...or maybe normal blowby and low engine vacuum due to radical cam. Depends.
I'm not a PCV fan. I don't like
oil in my intake. When it gets into the combustion chamber, it creates depostis and induces detonation. I vent the crankcase through large hose to an external can/breather and don't run PCV. My cam doesn't generate much vacuum; so a PCV system wouldn't work well anyway. And, the supercharger creates the potential for a supercharged crankcase in the event that the PCV checkvalve fails to seal. The same thing happens in a race engine if you have a little ring damage or blowby at WOT. Picture this...you're at WOT, blowby enters the crankcase, engine vacuum is zero (because you're at WOT) and the PCV check valve is being held shut by a weak spring and/or weight. If your crankcase is adequitely ventilated, the vapor blows out the breathers. If the breathers are not sufficient, some of the vapor blows through the PCV into the intake manifold carrying
oil along with it. That oil gets into the combustion, lowers the effective octane rating of the fuel, and now you detonate and damage the engine. Take this one step further into a situation where you have a badly hurt engine already...and it's a great way to finish it off. The excessive blowby will send significant oil into the intake, causing the thing to self-destruct ahead of schedule. I'd much rather vent to a can, and periodically see what's in the can...it tells me if I have trouble; hopefully early enough that I can do something about it before all my parts go to heaven.