Whew....!
Let me see if I can be nice here.
Uni-body is just a term, it could as well be "uni-frame".
There is a frame on the van.
The frame and the body are made (joined) together during manufacture. Just because there is no space between the frame and body doesn't mean there is no frame.
I currently have receiver hitches on two on my '90's GM vans, one '95 Chevy G20 (with the 33 gal tank) and one a '94 GMC G1500. They are bolted to the frame in the locations specified by the vehicle manufacturer.
Hitch companies have been manufacturing, marketing and selling hitches for these vans for years. They bolt to the frame.....just like the vehicle manufacturer (G.M.) planned and designed. That's why there is a towing capacity listed for the vehicle. And why the dealerships sold receiver hitches for them when they were new. They also sold step-bumpers for them. Some vans have both.....
I've heard that in some parts of Canada, unlike the US, hitches must be inspected after installation. That it has to be installed by a certified installer and that the hitch must be new. I learned this from some Canadian vanners who have receiver hitches on their third gen Chevys and they tow with them.
I sometimes use the GMC as a basket carrier...
And we tow our little FunFinder with the G20, no problem.....