The Chris Houlihan conspiracy

I figure the likeliest theory is that Nintendo of America staff couldn't figure out how to get into the room to verify it was actually reachable. "The winner's name is in the game data technically, but we don't know if you'll ever see it" would be an awkward announcement to put in Nintendo Power.

I think Chris Houlihan is a real person who won the contest. It's way too specific a name to actually fake, and even if nobody won the contest, Nintendo Power likely would have extended the deadline or just forgotten it existed.

My guess is that Nintendo never publically announced the winner of the contest until years later either because he didn't want to be featured in a follow-up issue of Nintendo Power (or his parents refused to give consent), he and his family had gone into witness protection and had lost contact with NoA, or he had passed away shortly after the competition was won. It's also possible that he could have been a middle-aged man who didn't fit the profile of contest winners that Nintendo Power's editors wanted to feature in their magazine. Imagine that you're expecting kids to win these contests and your winner is a fat sweaty middle-aged D&D nerd.

As for why they chose a debug room... it's likely that the NoA localization team didn't do so on purpose. They probably looked at the Japanese text for an opportunity to add Chris's name to an NPC or room, found mention of a secret room and had no clue that it was intended as a failsafe which you'd seldom find in normal play. Jon Burton (Traveller's Tales) had used failsafes like these to catch any undetected bugs that could potentially cause a game crash and make the game fail quality control checks when getting Mickey Mania, Toy Story and Sonic 3D Blast past Sega. Nintendo also had a similar licensing/approval system, and I would not be surprised if their own first-party developers had added such a failsafe during development.

It's absolutely 100% plausible that somebody could figure out where to encounter Warmech and get an entry submitted. It's not like Nintendo Power asked for someone to beat Warmech, which would have been a vastly different story.

A commenter pointed out the text of the plaque supports the idea localization didn't know the context. It reads "I am Chris Houlihan. This is my secret room. Keep it between us, OK?" It reads more like dialogue to me since it introduces itself and asks a question, though it doesn't necessarily have to be dialogue. Could also be kind of like a "Chris was here" carving on a bench.