I think I tried this but it wasn't supported by our Exchange setup for whatever reason that I can't remember. I might try again at some point though...
Another option to try is davmail; it exports davmail/caldav/carddav/LDAP from an exchange server.
My only note with that is the caldav and exchanges internal handling of event invites will fight with each other, so don't try to accept invites from within your imap mail client.
