I think that the new Hummer is a real sweet looking vehicle. When I was in the Marines, I really got to see what these Hummers can do--offroad.
However, I will strongly disagree that these are vehicles suited for towing heavy loads for many reasons. I do have alot of towing experience and I really think this vehicle is a bad choice for towing that 42' Tiger. The tow rating isn't even close. My two main concerns would be not enough braking power, and the short wheelbase of the Hummer. The truck to tow a boat this size would be the FORD PSD, DODGE 3500 cummings or the CHEVY/GMC Duramax, especially getting the crewcab for the longer wheelbase.
If you have ever towed a heavy load with a "short wheelbase" vehicle, you will know what scary is all about. Wait until he tries to take that thing down a big hill and the brakes aren't strong enough and the "lack" of length of the wheelbase will have him swerving in 2-3 different lanes.
He is really putting himself, passengers and his boat/truck--not too mention other people at risk if he plans to use this Hummer to tow that thing.