I don't think any grad courses you take as an undergrad will count towards a graduate degree, because you are not enrolled in the graduate program.
To the OP, if the Master's doesn't take you out of the BS/MD program you're in and you'd like the extra year of experience/college before starting medical school, go for it! I'd probably skip it and go straight for medical school, but who knows, I probably would have been way too intimidated started med school at 20 years old anyway.