I got here the same issue. But because I didn’t get an answer I try it again.
I have a DC master, a DC backup and some DC slaves. Now I want to set up another slave in my DMZ but without Samba. I can do the set up and join it to my domain, but then it fails because of issues with dns. I guess the problem is because this slave has to have a ldap backend for bind and the other servers running with the Samba backend. How do I solve my problem?