There are some SMP programs that transfer credit to their respective medical schools if you matriculate there. One example is Rosalind Franklin's MS in Applied Physiology. If you get accepted for the following year, you matriculate as an MS1A--a first year medical student with advanced standing. If I remember correctly, medical coursework completed in BU's MA in Medical Sciences program also transfers over. I'm sure there are a few others.
Loma Linda has a small postbac certificate program that includes medical coursework, but does not transfer the credit to the med school if you matriculate there.
In the past I've heard of students testing out of medical coursework at some medical schools, but I don't believe it's very common anymore. I wouldn't expect medical coursework from one postbac program to transfer into another medical school, but it's not outside the realm of possibility.