ESRI ArcMonitor documentation clearly outlines use of either an active directory/domain or local accounts for running ArcMonitor agents and client. However, I'd suggest that ArcMonitor should develop resiliency for when a server is patched that is running either ArcMonitor agents or clients. The password of the ArcMonitor service account (for both local and domain accounts) is routinely 'lost' during routine patching of any server running ArcMonitor software.
I'd love for a way for ArcMonitor client/agent software to persist with the established service account password during/after patching so the service account running them doesn't need to re-authenticate post patching.