Do you remember in which of the books DD made the joke? When HP and the DA meet at the Hog's Head, the bartender looks vaguely familiar to Harry.
Not de ja vu. I actually am repeating myself.
Regarding Aberforth, it was never explicitly stated in the books that he was the bartender at Hog's Head, but Rowling confirmed the guess during an interview.
See http://www.hp-lexicon.org/wizards/aberforth.html