Puck wore a dress in "Props." Puck had said much earlier on that he could wear a dress to school and get away with it, either because he was a badass or a stud. He did not "get away with it," but got beaten up by hockey players. Like with how Kurt was treated, this is pretty indicative of how a trans* character would be treated. There's still no tolerance for cross-dressing at McKinley, as there wouldn't be in many American high schools.
Presumably Blaine would be a relatively well-informed ally to Unique. Blaine is just one person, though, and he's 5'8" tall according to the Glee wiki. The Glee wiki may be being generous there. It's not like Blaine could do much about bullying from jocks. Sam, Tina and Artie could be allies as well. I think things would be very bad for Unique at McKinley, though.