Oh... There is a small joke in our community about making money by developing graal.
http://www.valikorlia.com/forum/show...e-compensation
Basically Unixmad suggested that a foot up your ass is compensation enough for developing anything for Graal. I sincerely doubt they will feel you are entitled to any money for your time and energy.
That being said, you could always do this on the sly for a bit. I don't see any reason against subletting, to borrow a term, the game's structure. In that sense, it is no different than purchasing the rights to license a game engine.
And hey, if you're really successful, why not get off of this engine altogether, heh... NetGore is a pretty neat system, for example.