Thank you Mr. Tee, or thank General Hercules as he suggested it.

The quick answer to your question is
no, not in my opinion, primarily due to his stroke technique, and to confidence.
Now for the long answer...get a cup of your favorite beverage.

I think for the most part that Mr. Nadal simply had to get used to playing on these surfaces at a higher level and gain confidence on the surfaces against the better players. His advantage was that he was already at the highest level on clay against the best players by 2005, or even a bit earlier. So he already had confidence against those players. I would say he was very proficient on Wimbledon's grass between 2006-2008 as he made it to 3 finals against Roger Federer winning in 2008. He made the QF of the US Open in 2006 and the semis in 2008, so he was no slouch on hard either.
He grew up on clay. His Futures play consisted of 35 matches on clay (32-3), 0 on grass, 1 on hard (a loss), and 5 on carpet (undefeated by the way).
His Challenger surface play was more varied, but still predominately clay with 23 matches (18-5), 13 on hard (10-3), 0 on grass, 8 on carpet (6-2).
In my opinion, Nadal likes to have more time to prepare for his shots, especially as his big topspin requires a big swing. He is not as comfortable taking the ball on the rise. A fast serve by him only gets the ball back to him quicker. A slower more accurate serve gives him time to get ready. He seems to be more comfortable standing 2 or more meters behind the baseline. On higher bouncing courts like clay and many of the other hard courts like Indian Wells and Miami, standing further back gives him more time to prepare and he has more confidence hitting his topspin. The less confident he feels in his swing, the further back he stands, as close to the fence as he can get on some days.
Grass, by it's usual nature, is generally problematic for him, especially when it is fresh or soft from rain. The ball bounces too low to allow him to play as he usually does. It forces him to change his swing. Also sliced balls on grass bounce even lower and if it with sharper angle become impossible to play if he stands as far back as he would like. So he is forced to move in. Now at Wimbledon since 2001 when they changed the grass and soil composition, balls have been gradually bouncing higher than they ever used to, especially if London sees a dry spell. This has the effect of slowing play down, giving players additional time to react and allowing them to hit the ball higher in the strike zone instead of off their feet. It's the soil that gives this affect, as with the change of grass, it has become more dense (less air), more packed if you will, and less like loam.
Also, the affect of drier weather versus wet makes it's affect on the grass behind the baseline where a majority of players make their home these days. As the tournament progresses, the grass is worn out from use, and in drier weather is worn out even faster. By the second week, especially by the semis, it is literally dirt. This makes it much easier for players that use great side-to-side movement to defend. On fresh, more slippery grass, they simply can't do what they do on hard court or even clay. They can't take big long strides and plant their feet hard or slide with precision and change direction. If they try, they slip and fall down. Fresh grass requires and rewards great footwork, not great movement. Footwork are the little steps, the little adjustments you make as you move about. Shorter, quicker steps are rewarded. Many of the top defensive players of today don't have great footwork, namely Djokovic, Nadal, Murray. They have great movement for sure. Other players, such as Federer, have generally great footwork, can make small adjustments, with quick shorter steps and rarely do you seem them slip and fall, even on the freshest, more slippery grass.
So for Rafa, the challenge on grass is for him to survive the first week. He can do that against a majority of the lesser players that he plays against in the first week, but not all. Some players who use good tactics can make him very uncomfortable. In the second week it is generally more difficult to unbalance him. By then, it's predominantly dirt behind the baseline. The correct tactics to use in the second week against Nadal or other defenders with great movement, would be to play with more angles so that a Nadal or a Djokovic or a Murray is forced to run on the grass and not the dirt, or to play shorter slice shots and again force them to run and stop and turn on fresher grass and hit lower shots. Since not many serve and volley these days, the grass is generally still quite fresh from a meter or two beyond the service line to the net. Look at the Federer - Murray 2012 final during the 3rd set in the critical 18 deuce 5th game. Murray falls down 3 times in the one game, a technical knockout in boxing, but look where he falls. In the service box, and wide of the tramlines. The grass is still fresh in those places.
In 2013, I saw a different Rafa on hard courts than I had seen in a while, especially on the Cincinnati and US Open hard courts in the summer. His confidence was very high, and he played closer in than I've seen him, and was much more aggressive. This comes from confidence in his play. His timing was superb and he felt confident that he could make quicker adjustments and a quicker stroke.
I've probably gone on too long, Mr. Tee, I'll stop now.

Respectfully,
masterclass