Please note if you are using ZD's internal DHCP server, it would provide IP addresses to clients in the same subnet, provided you should have used default settings in the WLAN Configuration.
In the above case I assume you have used default setting (setting Access VLAN 1) in the WLAN that is the reason clients are getting IP address from VLAN ID 3; if you have configured it as VLAN 2 the clients will not be able to get IP address.
In the above case you need to use External DHCP server.
ZoneDirector comes with a built-in DHCP server that you can enable to assign IP addresses to devices that are connected to it. ZoneDirector’s DHCP server will only assign addresses to devices that are on its own subnet and part of the same VLAN.
Please use the below link to download the User Guide, and refer page 76.