There can be exceptions. I'm a non-trad, and had graduated from undergrad for several years before I applied. I took pre-reqs later on, but didn't take any non-science courses at that time. It didn't really make sense for me to get a non-science faculty req since i was out of school long enough that I doubted any prof would really be able to say much about why they thought I would be a good candidate for med school. I substituted with letters from a more recent employer in the field of study of my undergrad degree, and a letter from a supervisor at my current job. If a school required (and at this point I can't think of who did) a non-science faculty letter, I emailed them to tell my situation and all were fine with that substitution.