3.0 undergrad (ie, not stellar by any stretch)
Valedictorian in MBA
Worked a couple years
Smoked a post-bacc and the MCATs while doing some research
Now, two years left in an MD/PhD at a decent place (that I love)
It can happen, you just have to package it right. In reality, I don't think having the MBA helped. Rather, doing well in the post-bacc was probably more important (and the MCATs) as adcoms could understand and evaluate that better (most didn't get what B-shcool was about). Some grad bio classes MIGHT help if the masters is in a somewhat distant field.
Just my thoughts/experience.
P