It isn't compatible. NES controllers use a shift register/encoder to encode the buttons over fewer wires than one common plus one for each button. SNES controllers are NES compatible because they basically cascade two of these shift registers per controller. The NES Four Score does something similar. The NES Satellite simply encodes that same data into IR.
NES Zapper, on the other hand, uses a pin inside the controller port that has nothing to do with the encoded buttons. The NES Satellite does not do anything with this pin. It doesn't encode it, it doesn't see it, and it certainly doesn't replicate it on the receiving end.
