If you have admin support you are NOT an underground anything. You are just not recognized as a Greek group. Don't make it worse than it is.
The admin is gun-shy about adding Greek groups; however, I would point out to them that just recognizing you as a "club" means you can select and train your members however you choose. If you are a sorority, recognized by panhel, you will have to follow Panhel rules which are more rigid. It's to their advantage to recognize you as such.
Unless of course it's the Panhel members who are voting you down, but it doesn't sound like that. Is it?