Minions of the darkness doesn't mean they are actually darkness. There has only been one "darkness" creature so far in destiny and that was in the black garden. Don't you remember the black cloud at the end of the story? That is the darkness and there are more then just one. If there weren't, the game would be over as the traveler would have no other enemies hunting it. But, again, the fallen, vex (especially), cabal, and hive only use the darkness, they are not darkness. Just like guardians use the light, they are not the light (traveler). The vex are not the same race as the darkness as the vex worshipped the darkness as a God, because, even with their far reaching intellect and understanding of time, they were still not able to comprehend the darkness itself.