Tieflings are Outsider (Native), which means they’re native to the Material Plane. ToM’s Dark Creature template makes a creature extraplanar when not on the Plane of Shadow.
To me, this seems to imply that the creature is native to the Plane of Shadow, which implies they’re not native to the Material Plane. Does anything actually happen to their Native subtype, though? Which is to say, are they treated like a non-Native Outsider for the purposes of eating/sleeping/raising?