I have an e-smith gateway working with an airport base station connected so that our macs can use the wireless networking.
Our Base Station is connected to the hub, in the Airport Admin software, we have allocated the base station an IP address that fits in with the e-smith server, ie, 192.168.0.66. The Base Station is set up to provide IP addresses via DHCP to the Mac clients. I have had no problems with this setup, it all seems to work very smoothly.
We have NOT got DHCP running on the e-smith server though, I did read somewhere that you should only have one DHCP server on the network!
Hope this helps a little