Great question... you can uptime vfiler0, but not in a vfiler itself. You can infer from the vfiler0 uptime, however that won't account for a vfiler that was stopped for shorter uptime than vFiler0 or conversely a vFiler that continued to run after a takeover/giveback cluster event for a longer uptime than vFiler0.
If anyone knows for OnCommand it will be Adai, but will see if I can find anything (he'll know off the top of his head I am sure though).
