There are any number of common as well as specialty substances we use in the darkroom which might be utilized by dopers and drug labs. The DEA simply wants to keep track of how much goes where. If unusually large amts of a suspect chemical are being sold independent of those other chems which might typically be used in photography, they naturally are going to ask why. Dope is made from all kinds
of things. In Holland they smoke vanadium salts and other heavy metals which might be used in alternative photo processes. A few people do it here (or did it here - can't imagine they live very long!).
The DEA knows what it is doing. No big deal, and certainly no serious inconvience to anyone using these
chemicals legitimately. None of us wants to see our distribution supply hampered or cut off by someone inadvertently selling something for illegal use. That's why this kind of information has to be collected.