I feel like the Darkness is somewhat like an infection. What I mean is that in some of the descriptions it says the Darkness gives powers to the enemy species. Over time the Darkness corrupts the enemies, and changes the organic parts of their body. So in this case Dregs become Thralls, Vandals become Acolytes, and Captains become Knights. For Hive Shriekers, they seem like Servitors that have some extra plating. Hive Ogres seem like Cabal that are corrupted by Darkness. Due to them being so big, the Darkness changed them so much it gave them "space magic." The Vex are robots so they don't really change due to the Darkness. The wizards seem like the only native Hive, and they are responsible for corrupting the Fallen and Cabal. Also in the Beta story, it seems like all the Ghosts, Vanguards, and the Speaker fear the Hive the most, because they signify the coming if Darkness. So yea this is one of my theories about the Hive.