Sorry, I don't quite qualify *yet* as a successful non-traditional applicant w/substantial post-bac coursework, but feel somewhat qualified to answer based on my conversations with numerous admissions committees over the past several months.
Essentially every school has a "first screen" based on numbers alone, if you don't meet or exceed these numbers, your application is not considered. This is based on both grades (UG and science UG), and MCAT minumum scores per section. If you don't clear a school's "threshhold" in BOTH categories, you will not be considered, i.e. in speaking recently with a private school in the midwest, a single section mcat score below 8 will cause an applicant not to be considered regardless of GPAs, at another public midwest school, the cutoff for out of state applicants to be considered is 35 MCAT and 3.8 GPA. Based on my conversation with this school, they want in-state residents almost exclusively. At a very friendly school in the southeast, the director of admissions told me that they'll consider seriously any candidate with a 3.6+ GPA undergraduate and 10 per section MCAT.
So the shorter version is that both the grades and the MCAT must meet the threshhold, each school's threshhold is a bit different (and often depends on your "ties to the state"), which makes it tough to provide a general yet accurate answer to the question. I'd suggest speaking with the schools that you're interested in.
