Answer from jtac:
Action Plan:-
-I saw the message and the site url where you saw the message.
-The message on the url means that the you need licenses for deep Inspection on all the device in the cluster.
-You cannot use license on the master on the back-up device for the Deep inspection functionality.
-Deep Inspection can be implemented on all the devices in the cluster.
-Following is the link for the verification:
http://kb.juniper.net/InfoCenter/index?page=content&id=KB4918&cat=NS_500&actp=LIST
So DI in active/passive cluster works, note in the original kb is weird...