I interviewed there early last December and got the acceptance phone call last week! I think the reason you don't see much about UMD on SDN is because they only interview around 150 students for 60 spots. Add in their primary care focus, and you really don't pull in a large SDN demographic...
The interview is very low-stress. It is a great opportunity to add your personality into your application materials. You should also expect to explain why you see yourself becoming a rural, primary care physician. They are very up-front about this; it is, after all, the goal of their mission statement! As far as interview format, there are two interviewees. Each person interviews with two different admissions committee members for about 45 minutes to an hour. Afterward two current students host lunch in the cafeteria. They also give you a quick tour of the Medical School, although with 60 students it's not exactly a sprawling facility.
Good luck with your application! 🙂
Barry