I think it's a coincidence that the Thralls and Dregs/Vandals look the same it's possible that they originals wanted the Hive to be space zombies that resurrected dead species like the Fallen. However if that was the case they'd be adding humans and guardians to their ranks along with the Cabal but they aren't. If you look at the Hive they all appear to have exoskeletons, They have rooms filled with egg sacks ,and have a tiered hierarchy like a monarchy; you have the Thralls which means slaves, Acolytes meaning assistant or follower, Ogres meaning hideous man eating monster/giant, Knights meaning someone who serves a sovereign lord, Wizards meaning someone with magical powers. The Hive sounds a lot like Arthurian legends by that tier system and since they're the "Hive" which is something created by insects and going with their exoskeletons, egg sacks, and tiered hierarchy everything points to them being insects so they must have a King and Queen that we haven't seen. Also I just remembered if you kill a Wizard the other Hive under them usually die so they must have a psychic link or something similar to what most insects have and the Wizard with their powers are a lightning rod for that link picking up the signal from the Queen and King and sends it to the Hive beneath them and vice versa so when the Wizard dies and the Hive dies with them that's because that psychic link shuts down and they don't actually die but go into a hibernation state until another wizard comes by.