I think the fact that the device was added as universal device is the reason it's not going to pick up the APs. The thin AP discovery portion is triggered by adding the device as a known controller type, so in this case it'd be as Aruba Device from the Device Setup -> Add menu. You'll want to delete the entry that's showing as type universal device and then re-add as the Aruba Device. Once that's done, the thin APs will show where the system is defined to place them, so on AMP Setup, there's a setting for where to put thin APs, by default this is the 'new devices' category. From there you'd either add it to group and folder, or pre-define it to auto add based on your preference.