After completing a surgical residency and fellowship, I can say that never did I do or hear about someone having general surgery getting a full pelvic exam. That doesn't mean that exams under anesthesia are not warranted (we do plenty of those for perianal reasons) or done, but in general those exams are the realm of the Ob-Gyn, not general surgery. I have opened the introitus when looking for the opening of a perianal fistula and of course, for procedures for recto-vaginal fistulas.
That said, if one was contemplating needing to do a pelvic exam, it should be contained on the consent form. Every consent form I have seen contains a phrase like, "I authorize Dr. X and his designated team/assistant, etc. to perform operation X..". Therefore, the patient is giving consent for the attending as well as others to perform the procedure named. It would be unethical to perform a pelvic examination on a patient without reason...those reasons are either:
a) standard part of the proposed procedure
b) findings during the consented procedure which necessitate a pelvic examination. All consent forms include a statement as well which say, "I agree to other procedures which the surgeon deems necessary" which covers the surgeon in case of unexpected findings.
There's a similar thread around here on this very topic (Clinical Rotations or Pre-Allo forum, I think). At any rate, while pelvic examinations for anesthetized patients who don't warrant them probably do happen, I would <hope and expect> that they are rare.
As a student, you have the right to refuse to do anything which makes you uncomfortable - this would be an appropriate reason, IMHO.