Make sure the server name and domain is valid in the configuration. The Dell demo box has the configuration wrong.
If we tried to netboot from this K2 the packet would contain k2000sandbox.cloud.kace.com.cloud.kace.com which is invalid and your Macintosh will not netboot.
The hostname should be k2000sandbox.
Instead of deploying ip-helper in the routers, I opted for a small linux box next to my RSA's VM running dhcp-helper. This allowed me more control. I have also deployed Raspberry PI's running dhcp-helper for buildings that have not been configured yet to allow our technicians to netboot and image their macs.