With a quality light, you really don't have to aim a shotty at an object to see what it is. You do have to aim in the general vacinity, but you don't have to sweep through the object.
Firearms instructors actually teach these tequniques using a weapon mounted light. Remember, a light spreads out as it leaves the lamp. It is not like a laser, which is a perfectly straight line.
Using a hand lamp with a pump gun can be a little tricky to learn how to hold the light and rack the gun. Gives ya alot of stuff to fumble with.
Come to think about it, I think the sportsman channel still runs a show called Personal Defense TV. If it is still on, they have done shows on how to use weapon mounted lights on shottys, black guns, and handguns.
Using a hand held light is much easier with a handgun. One hand on gun, one on light.
With all that said, In a swamp, I would still away from a weapon mounted light. A head lamp sounds like a more user friendly solution.