With special fx, body doubles and computer graphics, Hollywood can pretty much capture anything on film and make it seem real. Tennis wouldn't be any more difficult than, say, learning to dance like John Travolta did so many years ago.
I read that Serena Williams was offered a part. She turned it down saying that she was too busy actually playing tennis to pretend to play tennis.
I think a "tennis" movie is a good thing. Same as football, baseball and any other sport we've seen in various films throuout the years. What's so special about tennis? I'm sure that those who play will flock to see how they're represented on screen. It's a first and long overdo, I say.