The ZoneDirector can serve DHCP on it's local subnet only, and the ZoneDirector assumes it's using default VLAN 1 (considered 'untagged').
Best practices advise customers to assign unique/different VLAN IDs to their WLANs (clients), and this requires that the ZD be connected to a switch that can Trunk more than one VLAN, each with its own DHCP server and def-gw IP for those subnet(s).
The ZoneDirector local DHCP is meant to provide a local IP to APs that are initially being connected (to learn ZD IP or Mesh info, and then can be deployed remotely),
*or* for the small business/home user, who trusts his wireless clients not to mess with his ZD/APs.