If GLEE were to perform on the Tonys, it would most definitely be fitting. It's a show that promotes the performing arts. AND they sing showtunes! (and the TV series has a host of theatre actors)
HOWEVER as it has already been pointed out, GLEE is not performing. Two cast members from the show, both Broadway veterans, are performing. And they are names that because of their association with GLEE will get more people to tune in. And that's a GREAT thing.
"The Spectacle has, indeed, an emotional attraction of its own, but, of all the parts, it is the least artistic, and connected least with the art of poetry. For the power of Tragedy, we may be sure, is felt even apart from representation and actors. Besides, the production of spectacular effects depends more on the art of the stage machinist than on that of the poet."
--Aristotle