Primarly this name is because they are ghost-type. But a spy also need to be invisible right? And futhermore, the fact that they are an ancient race is reflected in the name because of the sense of greatness and mystery that he inspires, a good comparison could be "The Old Ones" from Lovecraft. That could also mean that they are neither good nor bad, they just do as they want by influencing the other factions for their mysterious scheme, unseen from those whose life they control until the most favorable moment.