What you are saying makes complete sense to me. What I find interesting is that the DHCP offer message does make it back to the controller (as seen in the logs on the controller) but it is never delivered back to the client that requested it. If you watch the controller logs and wireshark on the client at the same time, you can see the client run DHCP discovery over and over and see the DHCP offers coming back on the controller but those offer packets never make the trip back to the client.
Running DHCP server on the controller may be the answer, but my company was purchased by another company that runs Cisco wireless so for now at least we are running both systems side by side in the datacenter feeding wireless to different parts of the company and they want both systems configured the same way which is why I'm trying to work this out. They claim to have Cisco working with the current configuration although I've personally seen it.