As part of the recent October 2015 PSU Patch release for Enterprise Manager, a list of recommended patches has been compiled for EM 12c. This list contains recommended patches for the EM infrastructure including the OMS, WLS, Plugins, Repository and Agent.
For more details and to review these EM recommended patches, refer to My Oracle Support Note titled Patch Requirements for Setting up Monitoring and Administration for Exadata [1323298.1].
Also, the information in the note contains not only a recommended list of patches for both EM versions 220.127.116.11 and 18.104.22.168 but also provides a link to a My Oracle Support Note that provides the steps for applying these patches. This note is titled Applying Enterprise Manager 12c Recommended Patches [1664074.1]. The patch apply process in this note provides maximum availability for the EM environment by structuring the patch apply steps so that the primary OMS server is up as long as possible.