You're going to run into a lot of confusion. There are as many definitions of "IME" as there are jurisdictions (i.e., 50 states, and each little federal jurisdiction). Usually, the term refers to forensic exams related to injured workers (i.e., workers comp). But there are several other definitions. And some people use the term idiosyncratically to refer to any civil forensic case.
Who can perform IMEs is dictated by each jurisdiction. Many states have registries of people who are allowed to perform these exams. Some of those states require providers to undergo formal training through the state or state recognized training providers. In many states, only physicians are allowed to perform IMEs. However, some states allow chiropractors to perform IMEs. Some states allow psychologists to do them. It really depends. You have to look up your state's requirements, or you risk practicing illegally.