EM is fairly DO friendly in some places, but the "top tier" academic residencies can certainly be snobbish. Of course, if your goal is to be a community ED physician (more clinical hours, no research, more $$$), there will be very good clinical EM residencies that will take a smart, hard-working, successful DO student. Over the past few years, the traditional EM residencies have had essentially NO spots left over in the NRMP match for the SOAP/scramble process, so EM is considered a pretty competitive specialty. Either MD or DO, a student who wants to go to a traditional EM residency program needs to do well in clerkships and sub internships, score reasonably well on USMLE Step exams, and pass the "2am test". (have to be able to be tolerable to a grouchy, tired attending at 2am). Doing 2 audition rotations at residencies that are a good fit can be very helpful, so just make sure that the DO school has had people do clinical rotations at MD schools with EM residencies.