Maybe I am not the right person to answer this but I'll give it a go anyways. I really think that these engines are very finicky about oil pressure and I am not sure that allowing it to breathe would be a good idea. Just an older worn out valve cover breather nipple on my car caused a month of really hard to diagnose idle problems.
At least on a T7 this posed a problem since I imagine the ECU was constantly trying to adjust to these inconsistent variables.
Saab went through 6 PCV system configurations on the 9-3 just to effectively get the blow by gases out without creating too much crankcase pressure. The past side effects from these older systems were leaking valve cover gaskets, engine sludge, and prematurely dead turbos.
If you vent too much you might screw up all sorts of readings and how the car runs. I believe that is why Saab went through so many design changes with the PCV system.. If you reverse engineer it you can see that not enough ventilation and you have dead turbos, excessive crank case pressure, and can also cause oil leaks all over the place because of pressure pushing everything out. Id make sure all PCV are clear, hooked up correctly and in working order. This will keep positive pressure in the crank case under control.