To the best of my knowledge, a WDH has two functions. The first is to remove some weight from the rear suspension components, such as wheel bearings, springs and shocks, if they need relief. The tongue weight rating you have indicated - 600 pounds weight-carrying - suggests that your vehicle does not need relief unless you put a lot of stuff in the Yukon's way-back area.
The second purpose of a WDH is to put some weight on the front suspension components. When you put a trailer on the hitch ball, the see-saw effect sketched out here
http://www.trailmanorowners.com/foru...&pictureid=441
removes weight from the front end. As you would expect, this can have a bad effect on handling (since the front end does all the steering) and braking (since the front end does most of the stopping).
The addition of weight to the rear end tends to push the rear end down. The removal of weight from the front end tends to make the front end rise. This is the diagnostic - the indicator - for the need for a WDH. Since the rear end of your Yukon doesn't sink much, and the front end doesn't rise much, and your weight ratings are OK, my conclusion is that you don't need a WDH unless the handling feels squirrely. The Yukon's wheelbase of 116 inches helps this situation. Just for the fun of it, you might want to measure the rear end drop, and the front end rise, and see if they are excessive. But I'm reasonably sure you are OK.
It should be noted that if the rear end of a tow vehicle sinks, and the front end rises, the vehicle can be returned to level by installing air bags in the rear. However, air bags do NOT remove weight from the rear end, as a WDH does. And they do NOT add weight to the front end, as a WDH does. They mask the symptom, but do not address the problem. We have a lot of discussion about this, but the conclusion does not change.
Bill