So I loaded the driver via the RetroPie script (thanks for that!), and then discovered that since I’m on a rev2 Raspberry Pi I had to load it with this command:

sudo modprobe gamecon_gpio_rpi map=0,0,0,0,2,0

At that point I still had no love running jstest. So then I tried using the 5v pin instead of the 3.3v pin, and there it was!

So now I’m working on figuring out the protection circuit that’s recommended so that the 5V doesn’t blow up the controller or the Pi. I think I get the idea using a 500 ohm resistor and a standard diode. We’ll see what happens next…