Ohh, I asked this numerous times to Melissa Melder, simply cause' my school wants the least hassle possible in regards to the program.
She assures that this 'mentor' role is almost completely inconsequential and 95% of the time, they never contact the mentor. It's only in situations where, for example, you were absent from your classes too many times in a row or didn't submit your assignments consistently that they contact this 'go-between' staff member.
She also assured me that they want as little to do with your school as well XD And more to do simply with the individual student. So your mentor does not have to be a staff member who knows anything about the subject, they could be from a completely different 'faculty' (extreme example: an Art teacher as a mentor for MUES Mathematics).
Hope that helps somewhat. ^^