Doesn't really matter, it's more up to Robin than whoever he faces on the other side of the net. Although the same could probably be said for Berdych. With Rafa you know what you'll get every single time, his lowest level of clay is still top3 if not higher but Robin's highest level of play would probably make him the favorite.
It's never up to Robin. Even when Robin beat an injured pain-killer-addicted Nadal last year he still needed a tie-break in the 4th set. If that match had gone into a 5th set you always go with Nadal for the win. That was despite perfectly heavy conditions and Robin painting the lines. In other words, if an injured Nadal wasn't far from Soderling's 'unbeatable' level then a healthy Nadal will win regardless of what Soderling does.