I don't believe that "pulling strikes" fools the umpires, but the ability to smoothly "frame" the pitch and give the umpire a good look can really help a pitcher. Jumpy catchers that are all over the place do not help the pitcher or the umpire. If the catcher is moving around to catch a pitch, that tells a lot of umpires that the pitcher has not hit his spot, and I believe, makes them less likely to call a strike.