Hi Chris,
The Host Attribute Default Gateway IP option is requesting the GW IP of the management interface IP which sounds like it's the IP of the interface your APs are connecting to. We recommend not using "admin" port/interface and only having 1 "physical mode", MGMT enabled interface on the controller, if you have multiples this could be causing an issue with determining which interface the controller should be using to send out STMP packets. You can also verify using packet capture utilities. Please give us a call if you still need further assistance with this issue.
Thank you.
Bill McIver
Global Technical Assistance Center
Extreme Networks