There are two oil painting techniques for figures. The first is to apply the oils directly over the primer, the second is the "oils over acrylics" method. Personally, I find the oils over acrylics method easier since you do not have to be concerned with color saturation, which can be an issue with the direct to primer method - depending on the colors being used.
So, if you are using the oils over acrylics method, then, yes, you first block in each color with acrylics and then paint your oils over this acrylic base. Be very careful to apply your oils in very small quantities (the underpainting allows you to do this more easily), and remove any excess with a clean, dry brush - no thinner. There are some other threads on this site about reducing shine, and you may want to look at those if a flat finish is important to your subject.
Good luck and happy painting.