Yay! Another theatre major!
To answer your question, it all depends on what part of the tec theatre major you are (my university has a Production/Design major, but different concentrations within that major).
If you're costuming major, there's several roles for you:
# Costuming Project Analyst
# Costuming Design
# Costuming Buyer
# Costuming Workroom
There's also a Costuming Host/Hostess role in that area, where you issue costumes at different facilities, do light laundry, etc.
If you're a hair/makeup design major, they have a Cosmetology Host/Hostess role where you apply theatrical makeup to cast members, maintain wigs, and can help out with parades and film shoots at the resort. With this major, I would probably also look at working at the Bibbidi Bobbiti Boutique.
There's also a Graphic Design role, a Disney Design Group - Creative Assistant role, and a Disney Design Group - Character Artist role.
That's it as far as theatre related roles go, from what I found on the Disney Professional Internship website. I would talk to either a Disney representative or your university adviser if those aren't what you're looking for.