Learning something new every day. I setup a few alerts for the NFS datastores in a lab and to my surprise, they won't fire up even when you unmount the NFS datastore. You would have thought vSphere considers NFS "storage".
But found this at the end :
How to create vCenter Alarm to alert on ESXi 5.5u1 NFS APD issue? | virtuallyGhetto
Was this the case with previous versions as well ? Always used FC or ISCSI so can't really remember ..