Looks likyou are missing the correct outer configuration. Add an additional IP helper entry to the router. Like you do it for a DHCP server.
The problem is that the client is sending out a PXE request. This request is a special DHCP broadcast. An IP helper will forward this to your DCP server to get a valid IP address but it is not fowarded to your PXE server – in this case t WDM server.
Before I bring what you said in the previous post to our network engineer, will this help if we are dealing with 3 different DHCP servers? All our locations have there own DHCP servers. The WDM enterprise server is at our main office where I am, its on our server VLAN with a static IP, we also have 3 software repositories at each site with there own static IP that is unique to each location so the DHCP servers at each site hand out IP to the WYSE terminal(mostly v90le).