To the best of my knowledge Paul only drums on "Back In The USSR" from the White Album sessions, and then "The Ballad Of John & Yoko" where John & Paul were the only Beatles around to do what John, in true form, wanted done while the inspiration was still hot....thus actually making it a Nerk Twins single. I'm 99% certain that it is Ringo on "Dear Prudence".
And YES Ringo's drumming on The White Album is just breathtaking. As I've said before here, he is my favorite drummer ever, and he fit my favorite band perfectly, and was one half of the greatest rhythm sections ever. Paul is a great drummer too (the BOTR album being the best example), and John & George can drum as well, but Ringo is the greatest!!
Om Namah Shivaya !!!!