Nice theories, the parts with the Traveler's past with the Fallen and Rasputin's actions are in all likeliness true. However, we don't really know the nature of the Traveler and the Darkness. Guardians are told that all the enemies they face are the Darkness. The story (if we can indeed call Destiny's missions a story) seems to imply that the Black Garden was the epitome of the Darkness, and that the Vex are the most devout minions of the Darkness. Of course, the Hive seem more related to actual darkness, so it shows how no concrete conclusions can really be made in this regard at this point.