I really don't know what all the options out there are. I think the forum system we use on this site, community server, probably supports AD groups for roles but to be honest, I'm not sure. Because there is no standard LDAP-based AD role provider with ASP.NET, you don't see people taking dependencies on that too often.
Still, I think it would be worth looking at. Of course, CS is commercial software. I'm not sure if you trying to avoid paying any money or not.