360 Gamepad Not Working Even with XINPUT selected?

I don't think remapping is supported, but the normal controls should work. That is dpad is mapped to dpad and so on.

Xpadder works by simulating keyboard keypresses with keys assigned (mapped) to your gamepad so it really should work with any program that uses keyboard input. Just configure rpcs3 to use keyboard as normal and then map your gamepad keys to the same keyboard keys using the xpadder program.