Everything I've ever studied about the PCV system says you need to flow fresh air through the crankcase to remove blowby hydrocarbon contaminants and moisture. Air flows in through the breather and out the PCV. That's why on every V8 I've had the breather was on one valve cover and the PCV was on the opposite valve cover. Without a breather and only a PCV you will create great vacuum but you will be dumping all the blowby contaminants and moisture into your oil.
A racing engine does not need a PCV. A breather definitely but not the PCV. In your case using a pump to create crankcase vacuum helps sealing for sure. Great for racing.
A PCV can just as easily suck air into the air filter above the carb, not the manifold below it. The vacuum may be less but there would still be enough to flow the system.
