I think you're jumping to conclusions here, F&B. It's true, many aromatic nitro compounds are toxic and/or mutagens. But many are not and are useful and commonly perscribed medications: clonazepam, nitrazepam, chloramphenicol are just a few examples. The nitro group in also not metabolized to the azo moiety of carcinogenic dyes.
The problem I can see with DON is that the NO2 gets reduced to NH2 in vivo, and this could well be an active metabolite since 4-NH2-amphetamines are known to be pharmacologically active. This metabolite could be the reason for the reported strong stimulation.