I did this on Z-Lab and am moving to a different system.
Yes, blowby gets vented because typically the crankcase is under vacuum (until you hit WOT & pressure = atmosphere), but air does not get circulated. You're only getting 1/2 the benefit of the PCV system. I change the oil in Z-Lab after every track weekend and the oil comes out black. I would expect even after a weekend w/ minimal miles that the oil would be somewhat brown, but that's not been the case yet. Since I change the oil basically every 200 miles or less imagine what it would look like after 3k.
You really also need to get the air circulated and then extracted in order to keep the oil from getting contaminated so quickly.