i don’t think its a bad idea until you try it and it does not work.
certain frames in the through the lens videos pimax used to shoot showed sde / pixels patterns, and there were previous images taken during kickstarter that showed patterns.
I think if correctly controlled you could probably get useful comparative information from them. I do think it would be important to have a rig built around a foam head or some other way to set the camera distance at the eye distance for each headset, as simply putting the camera sat 30 mm from the lens for all might not be a true comparison because the eye may sit further or closer to lenses in each headset .
I would definitely like to see the result of that photography.