the usual method for using the wireless on a router in a network with an existing DHCP server is (after turning the in-built DHCP server off) to plug an RJ45 from the network into the switch panel, (the bank of four RJ45 sockets, not the WAN port) it will then transfer the DHCP requests/traffic as if it was a wireless access point
remember to change the IP to a static address outside the scope range of the core, otherwise troubles lay ahead for your network!