Just a few thoughts I had but please have a read anyway and leave a comment.
{DIZ IS THE SUPERIOR}
In CoM Zexion comments that Riku's dark scent is similar to that of the Superior (leader of the Organisation). Riku's scent has was created by Ansem's possession of Riku. Diz appears as Ansem but Diz's profile says he is an imposter and so therefore I concluded that Diz is just using Ansem's battered body (remember Ansem cast of his flesh to join the darkness) since Diz doen't have a body of his own. When Riku meets Diz as Ansem he can 'smell' him so to speak and doesn't smell the scent of the same darkness as Ansem's on Diz since Riku has the same dark scent as Ansem. However Riku first believes that Diz was Ansem. So maybe this proves the Diz is the Superior since his scent resemble's Riku's but why would Diz be following Riku's path throughout Castle Oblivion?
{DIZ AND AXEL WORKING TOGETHER}
Another possibility is Diz is working with Axel to bring down the Organisation and both are trying to use Sora and Riku to do it. That would mean that Axel is the Unknown in the screenshot talking to Diz which means Axel is a double agent of sorts.
Sorry if you don't really understand the first theory but I'm a bit tired so my English isn't that good at the moment.
{DIZ IS THE SUPERIOR}
In CoM Zexion comments that Riku's dark scent is similar to that of the Superior (leader of the Organisation). Riku's scent has was created by Ansem's possession of Riku. Diz appears as Ansem but Diz's profile says he is an imposter and so therefore I concluded that Diz is just using Ansem's battered body (remember Ansem cast of his flesh to join the darkness) since Diz doen't have a body of his own. When Riku meets Diz as Ansem he can 'smell' him so to speak and doesn't smell the scent of the same darkness as Ansem's on Diz since Riku has the same dark scent as Ansem. However Riku first believes that Diz was Ansem. So maybe this proves the Diz is the Superior since his scent resemble's Riku's but why would Diz be following Riku's path throughout Castle Oblivion?
{DIZ AND AXEL WORKING TOGETHER}
Another possibility is Diz is working with Axel to bring down the Organisation and both are trying to use Sora and Riku to do it. That would mean that Axel is the Unknown in the screenshot talking to Diz which means Axel is a double agent of sorts.
Sorry if you don't really understand the first theory but I'm a bit tired so my English isn't that good at the moment.