This is cool, the storyline they've chosen fits into the manga and the anime, so it fits both parties. The only problems that could occur now is super saiyan 4 being present, if it is I'll slit my wrists or something.

Ooooooh, I wonder how the hell fusion would work...

Seeing as how Saiyan's are like the most powerful race in the game, why play anything else? Plus you'll only be able to get some very necessary SSJ action with a Saiyan.
My guess is that saiyans have intergrated with the human race by now, meaning a human would have to earn the super saiyan ranks, or some entirely new 'forms' that would be of equal power to perhaps some namekian forms. *shrug* They wouldn't make the races unbalanced.