My school offers Guitar lessons for 2 to 4 credits and you receive a grade and it is calculated into your GPA. Does this also count for medical school as well?
Any course you take "counts" toward med school in the sense that it goes on your transcript and application. Whether it means anything more than that really depends on who is looking at your application.
The grade you earn is included in your application GPA unless you take it P/F. Then, even if you flunk, there is no impact. But the failing (or passing) grade is listed among your other courses.
What they said. Anything on your transcripts that has a letter grade gets calculated into your GPA and can be seen by an adcom. If you're worried about bringing down your GPA, take the class P/F.