Eckerd College has a nice theater program. They put on at least 2 plays per year and are open to theater and non theater students. In addition, Eckerd is home to a small local theater company. They have a noted improv group too. The students are most definitely not preppy.
Check out this other thread, about poly sci and theater: http://talk.qa.collegeconfidential.com/parents-forum/2122601-double-major-or-minor-poly-sci-and-musical-theater.html#latest There is some info in there that might help.
I agree on contacting departments. We have done that with dance as my kid does not want to major but wants to dance. There are lots of colleges so using the EC as a filter has worked well for us (so far).
One comment about contacting the departments. Trust but verify what they are telling you. We had a few schools where there were big disconnects between what staff told us vs the students.