As an inspector, one has a duty and an obligation to enforce the rules of the NEC in effect within one's jurisdiction. The interesting component of these types of issues, is the compelling urge when something like this comes up, for an untrained inspector to "read between the lines" and superimpose an interpretation that lacks clarity, just like the code intent of the specific provision might lack clarity. This is double-trouble. This is where an inspector without proper training makes up rules because he/she can't understand the rules in question. This is done a lot in my area in upstate New York. 3rd party inspection agencies hire inspectors without training and communities by and large are not requiring any demonstration of competence. I live in a rural area. Not necessarily up with the times.
With regard to this specific example of the electronic unit installed within a cabinet I can understand the concern. 110.3(A) points out terms like "examination" and "suitability". It says (in an unenforceable fineprint note) that "suitability of equipment may be evidenced by listing or labeling". There are a number of considerations under 110.3(A), not the least of which is (5) "heating effects" and (8) "other factors that contribute to safeguarding...".90.4 states it's the AHJ that has the responsibility for making interpretations.
It almost seems like in this example, the AHJ will be "granting the special permission contemplated" by doing his/her best to understand the unclear rules.
But, most importantly, IMHO, there is not a clear mandatory provision that specifically prohibits this un-listed, un-labeled equipment to be mounted in the cabinet, providing all other rules are maintained.
