Paul, I wouldnt worry about rating it for rescue... Just put in the instructions "not for rescue purposes".
In all the rescue classes I have ever taken, albeit only a few but more than none, never has it been prescribed for a rescuer to move to the victim and then use the victims system to lower both themselves and the victim. Primary rescue most often either involves adding the victim to your system, in which case it should be rated for rescue, or using both yours and the victims systems in tandem to lower the victim to the ground.
It would be easy enough to choose a different method to access the victim and bring them to safety.
If someone did decide to use the HH to facilitate a primary rescue, chances are it would work just fine IF they modified their hitch as you would in any rescue scenario. Classes teach that you should add extra raps to a hitch when using in a rescue to compensate for the extra weight, the hitch cords are not rated for 2 people, or even close to 10k lbs.
I believe if you properly word the instructions/ratings you would be protected from liability in that case.