BuddyPress.org

Although WordPress / MU use its own WP authentication methods, I would state that LDAP will never be a plugin module for BuddyPress.

BuddyPress is a plugin for Social Networking – asking it to deal with authentication is like wanting your office document application to play mp3’s.

Authentication however – within WordPress / MU is pluggable and if there is a plugin out there that supports LDAP, then give it a go as BuddyPress will only check if you are logged in or out and has nothing to do with authentication.