This is normal discovery process like other FMW targets.
1) Install Agent on Target Host where UCM/WebCenter is running
2) Deploy FMW emas plugin to Agent
3) It should automatically discover your UCM/WebCenter target, if not then you can use auto-discovery results from EM 12c console.
4) Setting up notification/incidents is same as we do for an normal agent/host/database target.
Configuration Assistant: Enterprise Manager 12c Cloud Control Incident Management Rules and Notifications Methods (Search Helper) (Note 1541634.2)
You can add in 12c console by navigating to TARGETS > MIDDLEWARE > ADD > Oracle Application Server.
Once you add the target you will need to configure notification in console. You will need to create specific incident rules for your target down/unrechable scenario.
12c Cloud Control: Steps to Configure Email Notification Method (Doc ID 1368262.1)
12c Cloud Control: Steps to Configure Incident Rules to Send Notifications or Manage Events / Incidents / Problems (Doc ID 1368036.1)