This isn't technically a hack - it's a custom Action Replay Max save file that uncovers an existing (but hidden) element of the game. When Tecmo made Dead or Alive 2: Hardcore for the PS2, they included a nude Kasumi polygon model, but dummied it out during normal gameplay.
Hacks for Xbox title Dead Or Alive Xtreme Beach Volleyball that strip all the DOA girls naked have existed more or less since the game was first.
Dead or Alive Extreme Beach Volleyball tech work, proving that nerds will go to any length to see a naked girl. Every iteration of the franchise has seen more than a handful of unique hacks to get her clothes off, but we felt.