Nintendulator SNES controller

Nintendulator appears to support SNES controllers. Are there homebrews that require it? Is it based on some way that you can rig up a real SNES controller to a real NES?

The SNES controller is compatible with the NES by design, it's just the plug that isn't compatible. If you build an adapter or transplant cables, it'll work just fine. NES games can read SNES controllers without modifications, and if they want to read the extra buttons, all they have to do is read more than the usual 8 state bits of NES controllers.

I'm not aware of any homebrews using the extra buttons in SNES controllers, but tepples has coded games and demos that can use the SNES mouse.

NES programs supporting Super NES controller
Almost all NES games should work, from both the original and homebrew eras. They see B and Y on the controller as A and B. But the only NES program I know of that's aware of the A, X, L, and R buttons is my spadtest tech demo.

NES programs supporting Super NES Mouse
These include the Meece tech demo, Thwaite, Action 53 menu, Sliding Blaster, and the Sound Effects Editor remake.

How to build an adapter
You can plug the controller as is into an FC Twin famiclone, as demonstrated in AWal's video. Or if you know how to splice and solder wires, you can build an adapter as described in Controller port pinout.

I typically use a SNES controller on my NES. I used the method of two cheap extension cables and making an adapter. Never had any issues with any games I played. If you were developing homebrew it might come in handy for debug button functions if you didn't want to use player 2's input. Or if it was a 2 player game.