No it's neither.
That screw is just to adjust the spring pressure at idle. If you have especially strong vacuum it can pull the valve open, so that's to tighten it up.
You cannot adjust the boost with the BOV, and the SSQV actually seals tighter the more you through at it because of the way it works. It's only when you let-off that there's an imbalance between the boost and vacuum side, and it pulls the valve open.