In the episode "?", Eko (in a flashback) goes to see about a girl who died and came back to life. She had a message for Eko from Yemi. You know, his DEAD brother Yemi. And by the way, in the tape of her coming back, if you listen, she screams John Lock's name.
All I know is that the writers are more often then not trying to throw us off course, they don't want us to figure it out until it's time to. So if an episode is titled "Dead is Dead" then maybe we need to "?" that.