I am going to challenge SAM and say that during my testing phase I had LDAP working with the hsql embedded DB. We decided against LDAP and only created a few accounts. LDAP was a pain to get working though, something with the syntax wasn't 100% kosher.
I may be wrong, my memory is horrible, but I know LDAP was working at one point, and I know that I NEVER work with SQL if I don't have to.