Dynamic Balance is simply balance in motion as opposed to static balance at setup. The visual balance system is pretty much inactive (although not totally) in the golf swing since it depends upon your head being in a normal erect spine position looking out toward the horizon. (Any decent ballstriker can hit it as well or almost as well with their eyes closed.) Since you are bent over and looking at the ground, it tends to not work very well.
Vestibuilar system is important, hence the need for a reasonably steady head, you dont want the inner ear fluid sloshing around too much. But most of the dynamic balance in the golf swing has to do with proprioception, the sense that you have of your overall body weight in or out of alignment with gravitys push or of a particular limb or body part. The feeling of balance in the feet is a constant though how much body weight pressure is being applied varies considerably depending upon which segment of the swing you are talking about. Eyes closed ballstriking is a wonderful way to train that sense of balance.
Some parts - Transition especially - there is certainly a pushing down feeling in both feet, especially the right foot for a right hand golfer, when you are in the Sitdown segment. Feet, Hara/Dantien or center of gravity two inches below your belly button, top of sternum or C7, knees and hands are the main centers of proprioception in the golf swing.
Jim Waldron