Medal of honor: heroes 2 has an on-rails mode that is fitted for the zapper just fine !
The point with vanguard is that you probably use the -, +, a and d-pad more than you would in a zapper game.
When you tuck the wiimote in the zapper those buttons wont be easy to use!
So my advice: Just try it out and see if it works!
You can also use the zapper for the wiiplay shooting gallery btw !