Any track is safe for beginners. I guess except Road America.
Anyway, Grattan is a very technical track. There are a lot to learn on that track even for a veteran. Lots of blind and off-camber corners. 1/4 mile straight and a jump in the back straight. It is quite a rollercoaster track. It is my favorite track in Michigan. Just go and have fun.
On the other hand, Gingerman is a true beginner's track. Very flat and lots of run offs. Almost nothing to hit except at turn 11.
Either one, you will have tons of fun and a lot to learn.
'03 BMW X5
'03 BMW ///M3