Griphook doesn't fit into the easy categories that the other characters can be shuffled into – he's neither good nor bad, neither pro-Harry nor pro-Voldemort. Rather, he's totally outside of this human conflict. As a goblin, he doesn't seem to care what happens. Of course, this does actually sort of put him in the "bad" camp, since the result of this battle between good and evil will dictate what happens to the world as a whole. However, he does provide invaluable help to Harry and the crew, so we're grateful to him for that. On the whole, Griphook is just looking out for himself, and for goblin-kind – he has a code of ethics that simply doesn't match up with ours, as Bill comments forebodingly, and to try and hold him to human standards is kind of useless.