I don't see any rules against widescreen hack, but it's not the way the game was originally meant to be played, so I could see it being banned.

most of the time (if not always) hacks are banned for the OG game's leaderboard,so it's probably banned.

Oh yeah, obviously. "Widescreen hack" doesn't actually mean hacking the rom, just applying a graphics config option to make the emulator render outside the 4:3 resolution.

lostontheinternet is correct, the widescreen hack isn't allowed for the og leaderboard. Aside from allowing intro skip for category extensions, and some additional codes required for a few categories (nonstop, 1000/500 coins), hacks or codes aren't allowed for leaderboard submissions.