Haazen looks like Sion, is a Sith (kinda) and fits the whole backstory given to Sion thus far, but doesn't Haazen tell Lucien that he will train his sith and become Sion?

If you read the issue, Haazen calls himself Darth Hayze because he clouded the Jedi and no one suspected him of foul play (a KOTOR Palpatine ) He does joke about naming Lucien Darth something-starting-with-L or Darth Sion, but it was too early to make anything official. We'll see how the fight between Lucien and Zayne goes next issue.