Ok, I will do a short summary then and you will have to decide on your own.
A DNS server has “zones”. Zones can be configured completely different even on the same server. For each zone the server is authoritative or not.
UCS has its own zone (which gets created during initial install) which is replicated to all DNS servers in the domain: master, backup, slave. All servers are authoritative for this zone and any request for a name in this zone gets answered by these servers (found with IP or not found). No other servers will be queried. Never!
You can add additional zone by using the /etc/bind/local.* files on each single server. Be aware this changes only configuration of this single server and does not change anything on the other domain servers. Depending on the type of zone you configure (master, slave, forward) bind behaves differently. For master it is nearly the same as above. Except the zone is not replicated to the other servers in the UCS domain as it is only local.
For a slave zone bind starts an initial transfer and gets the full zone data from the configured master. Once transferred it will answer queries to this domain as it would be a master. Until the time-to-live (TTL) has elapsed. Then it will ask the master if there is updated zone data and transfers the zone again if so.
For a forward zone it will forward all queries regarding this zone to the configured forwarder.
If a query asks for a host from a zone which is not configured there are two ways. IF a (global) forwarder is configured it will ask this forwarder and forwards the answer to the requesting client. If not forwarder is configured bind will discover the authoritative DNS server for this domain by top-down and asks for “.de”, then the server for “.de” will be asked for “.beispiel.de” and finally this authoritative server for “host.beispiel.de”.
I do not know how you have configured SPZ on your DNS. If it is just a zone configuration you might configure UCS DNS to take care of it and configure the zone on every UCS-DNS. But I guess if might be easier to configure EVERY UCS server to use this DNS as forwarder by
ucr set dns/forwarder1=<IP of SPZ DNS> and
ucr set nameserver1=<IP OF MASTER>; ucr set nameserver2=<IP OF BACKUP>; ucr set nameserver3=<IP OF SLAVE>.
Thus, alls queries not regarding you domain zone will be forwarded from the dns server to your configured forwarder how takes care of the SPZ configuration.
[EDIT] And you should make sure all yur clients will querie only the UCS nameservers! Otherwise request for UCS zone will fail.