No, it isn't off limits for Catholics because of dress. You're more covered, actually, in ballet class (even though the clothes are formfitting) than in most athletic disciplines. In performance, most of the costumes are built over nude colored liners that cover the chest completely. You can't see that from the audience. Think about it--would anyone be able to assume the extreme positions and actions required by ballet in a completely strapless and backless tutu without it falling off?
I danced with New York City Ballet for twenty-two years. We had quite a few practicing Catholic dancers, and I was blessed enough to have been the RCIA sponsor of a fellow dancer who converted from Presbyterianism. Additionally, there is a Jesuit priest who danced for awhile at Boston Ballet and is now the head of the dance department at Boston College. Like all performers at that level, he danced in the relevant male costuming when onstage.
I doubt the Jezzies would let one of their number perform if ballet was considered immoral by the Church, but his superior approved his stage career. Naturally, performers have to be discerning and discriminating in the roles they accept, but the big companies generally shy away from the more provocative stuff.
Classical ballet is a marvelous art, and when I think of Theology of the Body, I can't help but recall my performing days. Performance at that level is truly a prayer if approached correctly. And one of my favorite dance-related quotes is from Albert Einstein who said, "Dancers are the athletes of God."
Most dancers don't wear dance wear outside of the studio, unless they are en route to class or home from class. We're pretty swaddled up, even in hot weather, to keep those muscles warm en route to, and we're in a hurry to get that itchy, gamy stuff off and hop in the shower afterward. If you see someone on the street with a leotard on, it's a sure bet she is NOT a ballet dancer!