Also got this letter.
Duke has some dual degree programs that are really, um, *unique*; I think if you apply to do an MA in their plain-jane graduate school of arts & science, your regular application materials for the law school suffice. These are for like history, econ, etc. But if you want to do a joint MD, MBA, MPP, etc., additional apps are required to those specific schools. Your question's a good one...they aren't going to let you into med school w/o your MCATs.