Here’s my guess about how the limits work:
Putting weight on the hitch does two things. It adds weight to the TV, and it takes weight off of the front axle. The payload limit tells whether you have added too much weight. The tongue weight limit tells if you have taken too much weight off the front axle. A WDH hitch helps with the front axle weight.
So if a CAT scale tells you that the gross vehicle weight is within limits, the rear axle weight is within limits, and the front axle weight is close to what it was without the trailer, you’re OK.