Some post-bac programs have linkage programs, with guaranteed entrance to medical school if you meet certain standards. Others are designed for career changers, or GPA boosters. But they are outrageously priced. I designed my own post-bac, at my local state school and used my VA benefits to offset the cost. This was much, much cheaper, and I wasn't locked into taking any specific set of classes, within a short period of time. It allowed much more flexibility than some of the 18 month postbacs offer.
I was accepted to medical school this year, and the location of my postbac classes never came up. I think the only things that some adcoms are averse to, are online prereqs or those taken at a community college.