thats a gray area.....is it a biostats/epi professor (implying some mathematical/statistical inclination)? Or is it environmental health/BSHE/policy and management, etc? With the former I could possibly see, but the latter I'm not too sure, but I'd guess not. Plus, it might depend on the school, some schools are "MPH friendly" (like Tulane, according to a grad at CDC.) I'd say ask the schools you're applying to, but I wouldn't bank on it.
i'd agree with DW. i got 2 letters from public health profs -- one from a biostats prof and one from a physiology prof. the physiology is for sure a science letter. the biostats is too (if math is considered a science -- is it?). the same thing would be true for some epi course profs. i don't think international health, health policy, etc.. would be considered science. some environmental health classes might be depending on the nature of the course.