This jam doesn't explicitly mention it, but most jams say you can use anything that you legally have the right to use -- which means no sounds directly from existing, copyrighted games. If you do make a "fan game" that uses graphics, sounds, or characters from an existing NES games, you're in a legal gray area. Likely it'll be fine, but you do open yourself to Nintendo and other copyright holders complaining via a DMCA request, and taking your game down.