The AD Plugin will not operate properly if credentials are missing or are not valid. This monitor will report any Domain Controller Infrastructure Master that does not have valid credentials associated with it. This is the same information available in the plugin, but you can be automatically notified when there is a problem instead of having to check it manually.
The monitor is configured to only match agents with the "Domain Controller Infrastructure Master" role, so you can leave the targeting to all agents. If you only want to monitor systems that are under a service plan, you may choose to target a group such as: "Service Plans.Windows Servers.Server Roles.Windows Servers Core Services.Domain Controllers".
Thank You to @Jacobsa for the suggestion!