Start/Stop operations should not be shown/should be disabled for HDFS/YARN clients.
But as of Ambari 2.7, they are visible in Service actions.
Also there are multiple other actions which are currently enabled and are not applicable for the clients(listed below). These should be masked in the UI and not be shown to the user. Please clarify , if there is any discrepancy in understanding.
HDFS Client :
Manage Journal Nodes
Add new HDFS Namespace
Refresh YARN Capacity Scheduler.
Enable resourceManager HA