NFL Defensive Backs won't suddenly turn into wide receivers needing to run routes. Most baseball players won't suddenly need to pitch.
When teaching a gun disarm, the goal is to get the gun from the bad guy. Now what? You have suddenly become the guy with the gun. Go back to your rules about handling a gun:
If your student disarms the other guy, but starts waving the gun around at innocent bystanders, your student is still responsible for the ones he shoots, intentionally or not. With no gun training, how is your student supposed to make sure the gun is safe? Do they know how to put the safety on? Unload the gun?
Once you take the gun, the fight might just be getting started. If your student doesn't know how to use it, or how to keep it, it might get taken back from them. Or the guy, may have another gun or a knife...
Then there is the legal side. When the cops show up, your student would be the one holding the gun.
If you are going to teach a gun disarm... I side with Buka... you should first teach them how to use it, how to be safe with it, how to unload it, and what to do when law enforcement shows up... which involves knowing and teaching the local laws about weapons and self defense.