Let me restate: If "reside in a separate DIT" means a separate database this would be an awkward requirement.
I'd rather like to see another parameter which controls for which entries the constraints are enforced applicable within the same database. Similar to parameters unique_uri and/or unique_base of slapo-unique.
-- -- Howard Chu Chief Architect, Symas Corp. http://www.symas.com Director, Highland Sun http://highlandsun.com/hyc/ Chief Architect, OpenLDAP http://www.openldap.org/project/