I don't think you can use the AP cert for 802.1X as I ask my instructor on recent SWDI training at ATM17 and he said no it's not possible. I guess it's because we cannot have access or extract to the root-ca used by the controller to generate cert to the AP and import it to ClearPass. (I might be wrong here and missing some info about the process).
The only possible way I think is using PEAP. You can setup a username/password (could be a local account in ClearPass) and have the local database in your service. When you provision your AP there is an option for 802.1X using PEAP. (I never tried it but I would be intested to try it once my home lab is setup). You will probably need a fallback VLAN with MAC auth or something like that for new AP that are not provisionned yet or that need to be reprovisionned with PEAP where you can fingerprint that the device is an Aruba AP.