"Wiping out gender self-awareness?! Seriously? Hyperbole rarely wins arguments.

I would say that she's trying to broaden self-awareness. He'll still be a boy. He'll still know he's a boy. But he just might be a little more aware of his place in the world. Maybe. No guarantee. But if it works he'll be more sensitive to gender issues and also maybe better able to express himself if he happens not to fit into a rigid, predefined  role in society. 

Don't worry. A couple of hours a week in ballet is not going to turn him into one of those "nancy boys". He'll still play with boys outside of ballet class. He'll still end up being who he is - maybe more so if it turns out he's different than most.

And if he turns out to be a rugged, truck drivin' manly man, no harm done. Right?