There are Osteopathic physicians working in our local hospital here and I know several who work as ER docs in regular hospitals in other locations that I knew as docs in the Army (NG docs on 90 day rotations). They all told me that they were once not allowed to work in hospitals (which is why they are more likely to emphasize primary care even today) but none of them ever said that they weren't allowed in "real" hospitals to this day-that really surprises me.
My experience with them was 25 years ago in a small town in Texas. Both of my parents suffered terribly from their care or lack of knowledge. There were obviously restrictions on them at that time.