Nadal's best chance to beat Djokovic is ALWAYS on grass. That's where Nadal's shots penetrate the most, and that's where Djoko's backhand is the LEAST effective (the ball doesn't bounce as high on grass).
Given that Djoko dominated Nadal on grass, I think the result would be worse on hard courts.
Regardless of how Nadal plays, simply put, unless Nadal improves his backhand and adds more netplay/variety to his game, he will NOT beat Djokovic. The high short balls that Roddick was just defending against, Djoko will be creaming them for winners. The matchup has started to become waay more lopsided and it's become a mental issue, starting with a technical problem..