Adding Buddings with Active Directory

We are using OpenFire 3.6.4 with Active Directory integration. Logging in works great; however, I was surprised to find that buddies could not be added with their active directory credentials; e.g., domain\username. Rather, it seems that buddies have to be added with the XMPP domain; e.g., username@xmppdomain. Awkward.

Is this a symptom of the XMPP protocol, OpenFire, or the IM client (Pidgin)?

Is there a way to configure things such that logins and buddies can be referenced by their AD username?

Thanks,

-Michael