Garou are the fewest, by far. Their rage interferes with the smooth flowing nature of Do. Thus far only a handful of Stargazers have mastered themselves enough to learn even the basics. No brother has ever been around a Changeling long enough to teach them anything, at least as far as the Brotherhood knows. Vampires are a very special case.
Vampires have the patience and willpower necessary to devote considerable amounts of time to Do.
While their initial reasons for doing so are usually so they can gain an upper hand in physical confrontations, Do has a much greater effect on them as they progress. As the Vampire comes to accept himself for what he truly is, he finds his thirst for blood tapering off. It is theorized among some magi that Rank 6 would eliminate the Vampire's need for fresh blood entirely. However, since no Vampire is known to have progressed beyond Rank 3, this theory remains pure speculation. It should be noted that very, very few Vampires are ever given the opportunity to learn Do.