Though the truth is that they are not Zombies. It's more of a advanced form of possesing, where the body of the person that is being possesed is adjusted to the new soul, by completely coyping it(so that the old body would be the same as the new soul).
Why does the dead have to do anything ? Untill now ET proved that the dead can't change anything that is currently hapening. That's why I belive that Nagato and Itachi will both face Naruto as a test of his might, plus they may speak something usefull as well.