Yes cheating is a tough issue...and it is difficult and perhaps costly to ensure 100% compliance. This applies to many aspects of this hobby that I won't go into because that will take too much focus off of the tire additive issue.
I don't know the cost of the chemical sniffers, but they are likley expensive and only affordable perhaps for large races.
I think the less toxic chemical approach or just allowing one type of compound is too difficult to police, as it is difficult be sure that they are using the approved substance, even with chemical sniffers. I am for sure not an expert on this, so this would need to be validated.
But if you ban all additives, I think that is the easiest to enforce. In my opinon, it would be very difficult for someone in the pits to apply additives to their tires without someone seeing them do it. Also if you inspect tires to ensure they are dry, this goes a long way (although not foolproof) to prevent cheating.
The challenge of course is what does it mean to be "dry". This subject alone could foster a lot of debate. It would be in my opinion fairly easy to detect tires that had additives added and just simply wiped off, as these tires are still a little "wet" and/or "tacky". But if the additive was added the night before the tire would likley be pretty dry and not tacky and thus harder to detect. However if it is that dry and not tacky then is there any advantage? In my experence when I have added additive the night before using the tire it did have perhaps some advantage but not more than using a tire that I had already run that day.
Perhaps banning additives still allows for some level of cheating, but even if that was the case the cheating would be done outside of the track which would reduce the fumes the the track area, because a) the fumes that escape into the air during the application of the additive to the tire would not escape into the track facility aire and b) the tires would be so dry by the time they got to the track that they would not emit much fumes at all.
So yes maybe drivers will cheat, but the exposure would be reduced. Also it is not clear if this type of cheating would produce much of an adantage if any at all..only time would tell. And if it did and a visual inspection of how dry or tacky the tire is not good enough then for the large races we could use the chemical sniffers. Some of these major events cost $80k to put on, so if these sniffers are in the couple of thousand dollar range, is that really impossible to absorb into the cost of running these big races? At a race with 250 people a $2000 dollar expense is only $8 per person, which would only be required for that first event.