The boss appears, and may be killed, but neither his appearance (once the puzzle is solved) is recognized as a crew challenge nor his death as its achievement. There is no related icon on the map before or after his death. It should have manifested once I solved the puzzle, but it didn’t.
I think Judge Hightower is the Target of Opportunity? One Punch (who comes out after solving the puzzle) is a plain 'ol boss (like Urist McEnforcer in that same area).
Ah, I misspoke; One-Punch, though…now I remember: You have to kill him several times until he drops that shotgun—which I already have in my bank from a previous playthrough.