Are you using FTD or the firepower software module?
In case you are using the software module on your ASA you will only see health events that correspond to your module, not ASA itself. You may create a health policy and assign it to your firepower module to monitor its health.
FMC is not used to manage ASA with Firepower Services. If you use the new unified image (Firepower Threat Defense) you will be able to manage ASA using FMC but FTD feature set is still limited (e.g. anyconnect not integrated yet).
Let me know if this answers your question.