I would consider any ship carrying slaves as a slaver, if it's not lawfull and freeing them on the next base/planet.
The ID is some kind of an OoRP-Item, so it's meaningless. Only actions count, and the action is that he's a slaver. Shot him down and free them!
The idea behind that "can actively hunt slaver ID players" is, that OSC does not like slavery. Regardless of their ID. Whats the point in hunting a slaver ID player transporting gold, H-fuel or some other stuff like it?