First of all, examine the title of the hub this question comes from. Personal revenge or divine retribution. The only way divine retribution is truly authorized if it is exacted by a divine entity (i.e., God). Dante's quest for vengeance is an act of personal revenge to right the wrongs he felt were exacted upon him by people that he had considered friends or like-minded peers.
As for whether it is morally justified, that is an individual question and not a judicial one. The law does not provide for personal vendettas and vigilante justice, therefore Dante's actions would not be condoned by any judicial body, though if he were tried in a court for those actions, there are certain exculpatory reasons that could be given to present an adequate defense (heat of passion, for example). The ultimate answer rides solely on how each person who answers the question views what is or is not moral. Morality is also an individual issue.
I believe that Dante's quest of personal vengeance was justified because I believe in vengeance and retribution. I would rather exact venegeance myself than wait for karma to catch up with those who have caused some injustice in my life (even though I do have to wait since murder is, of course, illegal).