Found this nugget of gold hidden in some other section of the forums. Using USB Loader GX, I navigated to the game's settings (Samurai Warriors 3 > Settings > Game Load). I set Video Mode to Force NTSC and Aspect Ratio to Force 4:3. This enabled the game to get past the loading screen and enter the main menu.
Unfortunately, the game has further issues, which various backups have reported, including my own. Supposedly numerous people's backups (regardless of NTSC or PAL, from the reports I've read) still freeze on a black screen (black out) when trying to play different story modes. I confirmed this with trying to play Hanzo Hattori's story mode.