I dunno, seems to me they could take a stock vehicle, by stock I mean rebuilt to factory stock not a worn out vehicle, test it. Then install their stuff and retest WITH the same tires and rims as the before. Bumpsteer, ackerman, skid pad, G's and maybe braking distances could easily be gotten and not give any proprietary information away, which wouldn't be proprietary long anyway, it can be reverse engineered for the price of buying one setup.

Or one could use an existing known performer, Tom's Valiant comes to mind, and use it to test the new setup in a before/after comparison. Probably a reason some don't do it.