if you're referring to step 3, yes, you need an MD/DO to register...
certain states have requirements in terms of the # of months/years you've gotta do (post-grad training) during residency before you can take it, but SEVERAL have NO requirements (CT is a commonly cited example)...therefore, the loophole is that you simply register, after you graduate, in that particular state, but can take the test anywhere [i.e. the state you register in has NO bearing on the exam status, results, registration, ANYTHING].