This is a great question and unfortunately it's kind of hard to answer, because it varies from person to person. I was lucky enough to get a job at the Wheelwright Auditorium in the box office at the beginning of my freshman year. Due to that, I made quite a few friends who were not in the theatre department and they got me involved with outside activities. Even though I have since quit that job to work as asst. recruitment coordinator, I still keep in touch with them.
For the most part, yes, all the MTs room together. When you look at the current housing situation of my MT2014 class: I live with 2 other MT girls in my class and a freshman MT girl. The other 2 girls live together plus a BA Dramatic Arts major. 3 of our MT boys live with a BFA Acting major and the other boy lives with a Dramatic Arts major. When we move out next year, myself and 3 other of the MT girls in my year have an apartment together. Some people prefer NOT to do this as they don't want to come home to the same people they see all of the time. This is valid. My freshman year first semester I did randomized housing and lived with 3 non-majors, and had a fun time. I still see them on occasion. But priorities are different, and these girls are my family. We carpool to class, we do homework together, we rehearse with each other if we have scene work, practice for each other and get opinions, etc. Sometimes I want to kill them. And if that happens, I leave the apartment. That's the beauty. Although we went a whole year without any major tiffs and we still plan to live with each other next year. It's a personality balance too- there are MT girls I know in the department who I could NEVER live with. The 4 of us just happen to even each other out.
There are some theatre majors who are Greek. I can think of 2 freshmen off the top of my head- 1 is a BA Dramatic Arts major who has had an easier time of it because of the BA degree, even though she WAS cast in "The Laramie Project", and the other is a BFA MT female. I don't know how well it is going for her. I know that when she was in a show first semester she had a tough time balancing that with initiation, and that some people warned her it might not be the best idea. But if your priorities are in order and you can really keep up with that busy schedule, both of those girls seem to be very happy. Ken often advises against it, though, so he may have an opinion if he sees this post.
Edit: Oh! I also just remembered 2 male tech majors who are members of FIJI and absolutely love it. Tech is a little different, but they are probably (definitely...) even busier than the performance majors are. So kudos to them!
I often attend sporting events if I have the time. I went to homecoming freshman year and have gone to a few baseball games. But, in all honesty, you often just don't have the time. There is a student run theatre organization called "Upstage". I was secretary this year and will be Vice President next year as a junior. We are making a tremendous effort to start becoming a part of the rest of the student body and the CCU campus as a whole, instead of just being a party of a bunch of theatre kids doing what they want to do. We participated in and raised a TON of money for Relay for Life this year, working in close conjunction with the Student Govt. Association, attending their fundraising idea meetings and getting to know the other teams. We put on a production of "The Vagina Monologues" with the Women's and Gender Studies department that included cast members/crew who are non-majors. Next year we want to extend that even more, and we are making it a priority to recruit members who aren't theatre majors, but students who love theatre and might even have more time to make fun things happen. It's not just a performance vehicle, even though we do produce cabarets and student-directed shows, but a service organization as well, and we want the rest of the campus to know more about us and not think we're just "crazy theatre kids". Although you must know that one of my 2014 BFA MT boys DEFINITELY raised the most money in his drag and won "Miss Relay" this year. Was anyone surprised? Definitely not.
So, overall, it's difficult. I feel like any BFA program makes it difficult to remember there is an outside world. But when you are not in a show specifically, there are things to do and it is highly encouraged to live a little. You just have to take some initiative.