I've seen some outdoot NFT grows of regular vegetables, but not MJ grown hydro outdoors. It should work, but you can't control your stealth as well nor trigger flowering on your own.
Its not done often. I recently saw this one setup while reaserching aquaponics. I've only seeon one othertime when i guy had a tree sized plant in a bubbler bucket in his yard. http://www.overgrow.com/edge/showthread.php?s=&threadid=158118&highlight=aquaponics