The point of MAPSS is that you structure your own, entirely individualized curriculum within any branch of the social sciences. You absolutely have a concentration in a specific discipline, and on your CV you represent it however you want to - your transcript speaks for itself. Students are grouped by their chosen disciplines and are assigned to advisors who are in the final stages of their dissertations or are post-docs in their discipline. The program website actually has some very detailed information about the structure of the program, alumni PhD and job placement rates, etc. You should do some poking around.