Let's see
2011 WB F Nadal was a very nervous wreck, the guy started moonballing on Grass of all places but Djokovic had shellshocked him in to it.
If the same Nadal somehow turns up against any Federer it's a loss for Rafael. If the one from SF turns up, it still is a loss for Nadal but can be tricky for Federer. Remember even 2006 Nadal made his life difficult.
2011 USO for Rafael is 60-40 against 2005(Weak Backhand) and 2007 with 60-40 for 2004 and 2006 Federer( because of match up.)
2012 AO Rafael beats any Fed except 2005. 2005 Fed is a slight favourite.
2013 USO,more aggressive Nadal is actually something that Federer will like more than the energiser Bunny one. Aggression doesn't work on him unless it's strongman type, Rafael's play might actually make it slightly easier. Kinda like 2011 Djokovic was close to defeat.
2004, 2006,2007 Federer beats him.50-50 with others.
RG? um 2015 definitely goes down to 2005-07
Rest ? Only 2014 Nadal is in slight danger.
2007 Fed might be the best candidate to push it to 5 against 2014.
So life will be difficult for Fed, but not entirely hopeless.
Bottom line:
Match ups hurt.