they already do.
the "performance inspired" line is part funded by WME, is the UFC official supplement sponsor and hae all their products third party certified by informed-sport to be ped free..
but, these are not the kid of supplements the fighters are taking
PI do your regular creatine, pre workout energy drink, electroytes, post workout shake etc.. those are not the sort of "supplement" causing people to test positive anyway.
If all the fighters stuck to supplements like that contamination wouldnt be an issue
the contaminated supplements are things like testosterone boosters, mass gainers, the "supplements" associated with bodybuilding, NOT "dietary supplements"