This is from UMich's website...
Letters of recommendation are a significant part of your application, and you should spend some effort on this. Things to consider include, 1) how well the faculty member knows you; 2) the rank of the faculty member; 3) the course taken. We require three letters and prefer one from a science faculty member, one from a non-science faculty member, and one from another recommender of your choice. Letters from friends of the family, no matter how important or well known they might be, carry less weight than you might think! You may send additional letters if you want. Your recommenders should be individuals who can assess your personal qualities (such as work ethic, reliability, communication skills, leadership, compassion, and so on).
If fact...it goes on to say...
We prefer that you provide the non-science faculty letter as requested, however we recognize that in some cases such as the applicant who has been out of school for a number of years, getting such a letter may not be feasible. A substitution may be requested from the Admissions Office for any particular type of recommendation letter.
So UMich does PREFER a nonscience...
Here's the link:
http://www.med.umich.edu/medschool/admissions/faq.html#lor