Hi,
As per my understanding,
1. APs are connected to a Switch and Aruba controller is reachable from the AP.
2. APs are getting IP address from VLAN 1 subnet
3. There is one SSID on bridge mode and clients connected to this SSID are not getting IP , right ?
Please ensure the following cofig is in place,
1. The switch port where AP is connected should be a trunk link ( coz client traffic will go out of the tunnel) and VLAN 13 should be allowed.
2. As victor said, CPSec should be enabled in order to bring up Bridge mode SSID.
3.DHCP should be reachable from the switch where AP is connected ( Ensure the IP Helper is configured as per the requirement)
If you fulfill all the above, when a client connected to a bridge mode SSID, AP will forward the DHCP traffic of the client over the uplink port ( will not go through the GRE tunnel) hence DHCP traffic will reach the Switch where AP is connected.
Hope you got some clarity on this.