Yes. LDAP is a protocol. It doesn't care what the underlying storage DB is. So you could have a back-hdb master and a back-mdb consumer, etc.
Although I would note, don't do a subtree rename until all backends in use support it. ;)
--Quanah -- Quanah Gibson-Mount Product Architect Symas Corporation Packaged, certified, and supported LDAP solutions powered by OpenLDAP: <http://www.symas.com>