It would be helpful to find out what the professor’s policies are with respect to use of fraternity and sorority test files. The university might have a blanket policy on this. (Some students might spend a little time researching this by reading the university’s honor code on their web site; just reading the honor code will be an eye-opening experience for most students). Advise your students to research the use of fraternity and sorority test files on the university web site, or to discuss the issue with the head of the department or the chair of the university honor council.
Unfortunately, in this case, there is not much time. Researching the issue in the university’s honor code takes valuable time away from studying for the exam, which, if you do, could help you raise your grade and solve the whole problem!
Probably the best solution to this problem is “when in doubt, don’t.” You may not do well on the test, but at least you won’t have to live with the terrible consequences of being accused as a cheater. It should make you feel better in the long run that, although you may not make the highest grades in the class, at least you are not a cheater.