Not for the pure stroke, though. I don't hate Roddick at all even though I am not a fan, yet I admit that his service motion should be banned from professional tennis and used as an example for kids of how not to create your service motion. The potential for injury is just too high.
Same for Nadal's forehand, though not so much with the injury argument. Nadal has the power and balance to pull it off, but that by no means makes it a pretty or even technically sound shot. I like Nadal, but I wouldn't try to teach my child his forehand. His backhand is usually a thing of beauty, though.
Prettiness has nothing to do with "technique" and frankly I've never understood how people objectively try to argue such things with tennis. I fail to see why it is technically unsound though
Great margin for error, amazing spin, power, placement etc... Again, if it works as well as it does, why WOULDN'T you try to teach a player to emulate it, it's probably the main reason Nadal has 4 RG titles after all...