IMO:
Diz: Organization (or at least has a leadership quality towards it)
Heartless: none
Dusk: none
The heartless has no leader. I'm pretty sure they lasted long before they would have on (Ansem discovered the original heartless beneath his castle). Since they were born from the evil of people's hearts, couldn't it be that they are their own leaders? People didn't exactly create them (other thatn Ansem, but he created the artificial heartless).
But, the people who wield the power of darkness could manipuilate their minds and distort their brains to do their own bidding, since they are darkness? Like Riku, he created Anti-Sora from his powers, but he was not able to control them completely because they still appeared without him and when he was preoccupied.
There really is no proof that there is a "Dusk Leader". Just becasue there is one who can control the heartless, doens't mean theat there is one to control the dusk. Diz could be a possibility, but there has been no actual physical proof to tell so (correct me if im wrong).