Davis Cup does give 125 points if the player is from the winning team, and the said player has played 8 singles matches. I'm not sure if Nadal has played 6 already this year, but I feel pretty certain he hasn't.
Even if he did get the 125 points, he still would be 5 short (if he wins everything between now and WTF, and Djokovic sits out everything - both big asks, Rafa is still behind by 130 points).
So, in short, no...even a DC win wouldn't give him the necessary points
HOWEVER, if the above does happen, Rafa only needs to be in the SF at AO to get #1 rank back, coz he was only a QFist last year, while Djoko has to defend the title.
In fact, if Rafa narrrows down the difference to 1640 between now and year-end, then he just needs to be in the semis at AO to reclaim #1. Djoko would lose the ranking even if he won the title. And if my math is right, for Rafa to get #1 back by being a finalist at AO, he gets a further leverage of 1200 points, therefore if the points difference going into AO is less than 2840, then Rafa gets #1.
Although this is all speculation for now. Rafa is 4100 points behind Djoko right now, so a lot will need to go right for him and a lot will need to go wrong for Djoko for this to happen. But essentially, IF it were to happen, Rafa can only get the #1 ranking in Jan 2012.