MIL-SPEC aren't UL listed, but that's almost a technicality- they're subject to a far more thorough battery of tests. Using a plug as a disconnect for servicible equipment is standard, as in military applications, you can't always spend time looking for the breaker.
NEC doesn't require UL listing, though, just that that components be "listed"... and then cops out and leaves the definition of "listed" to be whatever the AHJ wants it to be.
