Yep he's back. SPOILERS once again, courtesy of Comic Book Resources.
"There was one “Dark X-Men” character that Cornell could talk about in some detail though. He's not a team member, he's a target. His name is Nate Grey AKA X-Man. The son of an alternate reality's Jean Grey and Cyclops, Grey first appeared in the 90's X-Men storyline “The Age of Apocalypse.” At the close of that storyline he found himself in the mainstream Marvel Universe where he put his vast mutant powers to work as a hero. During one of those exploits it looked like Nate sacrificed his life to save the world from alien invasion and “Dark X-Men” marks his return to the Marvel Universe.
“He's near omnipotent, the mutant shaman, and he's terrifying to my cast of characters,” Cornell said. “That’s because he's exactly what they don't want in play right now: a very powerful, charismatic, alternative leader of mutant affairs. And a Summers, to boot. X-Man is dreaming his way back into the world, the deadliest possible hero.”