While it depends on the particular program you are hoping to attend, most programs do not require the GRE. Of all the schools to which I applied, none required the GRE for admission unless you were interested in BME. Some schools make the comment that you might consider taking the test if you'll be applying for external fellowships (HHMI, NSF, etc.). So, if you plan to take the GRE anyway, then go ahead and good luck on it. It probably won't hurt your chances with MD/PhD, and could quite possibly help if you score well, especially in the subject tests.
I was told by a current MD/PhD it CAN be a liability if you do poorly. Make sure to take a practice test before taking the real thing! And usually, I think the general test is what schools are talking about when they say they'd like to see it, but aren't requiring it. The ranges would probably be the same as they are for admission to the graduate program, maybe a little higher, but GRE scores tend to be super-high at most MSTP schools.