Good question. I think that a graduate student who is studying musicology or composition may still be expected to have a major instrument and take lessons. I know of a top-notch school for such studies.
If you are able to skip taking Music Theory at an institution, by qualifying in that field by an exam or demonstrating your knowledge, instead look at http://www.musictheory.net. My adult employed student, already proficient in important works like Gliere and Handel, found that she can learn things there that her previous teachers failed to tell her, and she is happily working through theory knowledge on the internet instead.