Regardless of whether he is being paid, it is more of a safety issue and he should be entitled to more than a 15 minute break. But I always take a break if I am not being paid for it. My time is not free (there are times when I would sit at my desk to help out with overflow, but not actively do anything if it wasn't required).

If management want the machine operational in this time, they should be allocating someone to man in while your DH takes a break. IT is not your DH's fault there isn't enough staff there.

Even though your husband is just standing up for himself, I would try to encourage him not to do it in a smarta$$ way. If reduncdancies come about, that can be used against him (not legally) when management are making their decisions..