Jason, here's the thing about your statement. The prop hub can be out of balance and it won't matter much at all.
Why?
Because it is right on top of the motor. Right in the center of the spinning prop. What makes a HUGE difference is the further out you go from the center of the hub, the more imbalances affect the performance of the prop. At the hub, if the outer surface of the prop blade is spinning at 9,000rpm, the hub speed is CONSIDERABLY lower. At the center of a hub, it might be spinning at 200rpm while at the outer edge of the prop, it might be spinning at 9,000rpm.
Check out full sized helicopter blade balancing for a more complete explanation of how this effects props on a Quad.