From my experience *SQL backends are much more flexible and on the end reliable than LDAP.
Some years ago I used LDAP and it was really pain - access rights, change of structure, even simple dump/reload was problematic. Sure, most of the above mentioned comes from my "LDAP ignorance" - I'm not BFU but still can't use LDAP intuitivly. LDAP is simply "too different" than all other SW I use on day to day basis.
In your place, I would try to avoid LDAP and do some middleware between your DB and other services...