You're right, the original emulator source code (SDL chip8) is not distributed under GNU license, but under a kind of copyleft agreement :
Here is the original hearder :
Code:
/*This is my first attempt at writing a complete emulator
most of the code has been taken from a previous attempt of mine
that was intended to use Allegro but I never learnt how to use that libaray
anyway it is a chip8 emulator which is programmed to make
use of openGL and GLUT, the purpurse of writing this emulator
is to learn how to use openGL, GLUT, to write an emulator and
to furter expand my c programming skills and knowlage please
feel free to use bits of my code, all I ask is you give credit
were credit is due, TJA.
FEB 11, 2003. */
So, Zion can do what he wants with it (and port it to PSP for our best pleasure :P) , but i'm not sure he can release it under GNU license without the agreement of TJA :o :o :o