Hi friend,
Your requirement can be justified by using Aruba L2 deployment model.
Client traffic will hit the controller when you bring up a SSID in tunnel mode ( Client traffic will go through the GRE),
If you bring up the SSID in bridge mode, client traffic will not directly hit the Controller because in bridge mode there will not be any GRE for that BSSID.
You can choose the bridge mode as shown bellow,
If the SSID is in the bridge mode, Controller will be in the L2 deployment :
You can choose the VLAN for that client traffic as shown bellow ,
So once a client associated to the SSID ( Bridge Mode) then it will send a DHCP discovery in the mapped VLAN.
If you have configured the IP helper properly on the gateway, Client will get the IP from the respective VLAN.
Therefore here the controller is just taking care of APs nothing else.
Hope got clarity on this,
Please feel free for any further help on this,