The intel i spoke of suggested that there were 3 different intros (one for each species). The intro we have makes perfect sense for an exo but it seems a bit unlikely for humans or awakened. It´s one of the major story flaws that are discussed regularly. The rest of the ghosts behaviour represents a little hacking tool maybe it is even capable of reality manipulation or alteration of sort. But essentially there is a point in "hack a mummy to life again" making no sense i think. I did not state it as fact but unfortunately Bungie is more or less spongy towards this. I tend to be critical and that explanation just fits too good to be unlikely. It´s like surgery - if you cut something there will be a scar.