Not really, as NFS(v3) is a stateless protocol. The closest you can get, at least that I'm aware of, is the nfs per client stats. This will show you active NFS clients using your vfiler, but not which exports they are mounting, or which users are accessing them, I'm affraid:
vfiler context <vfilername>
options nfs.per_client_stats.enable on
options nfs.per_client_stats.enable off
vfiler context vfiler0
WARNING: make sure you turn client stats off afterwards, and don't leave running for more than a minute or so as it has a performance cost.