I just did this... the Zimbra wiki article seems to be a bit more relevant for me, anyway. You will want the patches referred to in this bug (for the Admin UI)... or I can give you what I have for the two files referenced (.
js files):
Bug 26423 – posix extension requires memberUid to contain a uidNumber
Anway, I have the same question.... should the BDC(s) also point to LDAP(Zimbra), or to the PDC, or what?
Chapter*5.*Backup Domain Control gives a summary, and seems to indicate that the BDC would also point to LDAP. I also hope to set this up soonish... whoever finishes first, add to this post.