Nitrile and touch screens. What is the distance required from your finger to the screen to make it work?
Even heavy duty nitrile gloves are a handful of mils thick (e.g., here), so you're unlikely to reach 20 mil for most gloves (roughly 0.5 mm).  Some do seem to peak out at 14mil, though, so you need to be a bit careful.   This paper talks about designing for glove use.  Techniques involve careful tuning of the capacitive field by tweaking the distance between touch screen plates, increasing the power output of the driving electrode, and minimizing cover plate thickness.

As to how to certify, that's probably tougher.  Microsoft offers a standard at this site that you might find a suitable starting point.  You might find it easier just to develop a suitable specification that satisfies your customers, developing a test, and meeting it.  Another option to consider would be working with a touch screen vendor to see what their standards are and whether they have a product that verifiably suits your use.