Currently there is no way to add the DNS partitions into the Samba database after the join has completed.
DsReplicaSync fails in this way:
../../source4/dsdb/repl/drepl_service.c:268: Failure - Failed to find requested Naming Context. werr = WERR_DS_DRA_BAD_NC
drsuapi_DsReplicaSync: struct drsuapi_DsReplicaSync
'samba-tool drs replicate --local' hangs in epoll due to a failed open (currently only tested with TDB) and the DONT_CREATE_DB flag.