I would say it could still work since the deck stuff is cutting out the messages to the conscious part of the brain, but signals must still be going back and forth on an unconscious level or else the decker would just stop breathing or similar. Yes, the body is pretty much out to lunch, so if your foot catches on fire you probably won't move said foot consciously though it may jerk back as the meat sears, but I could still see the hand in water trick provoking a flow issue since it is tied more into the automatic reflexes.
Netcat has been shown to hook up a catheter when going deep, because she knows she can't feel her bladder wanting to go, but the body will still perform functions even if the mind is shunted away behind that virtual curtain.
Or maybe Slamm-O! has done that hand in water trick to her before and doesn't trust his sense of humor going forward.
Edit: To date though Mythbusters have busted the myth that putting someone's hand in water causes them to urinate, so holding with MB it wouldn't cause it regardless if they are in VR or not, but still makes a good prank to pull in game.
