The feat trigger is the enemy entering the square, not moving into the square. Because of the wording on the feat, even if the enemy was slid/pushed/pulled into the relevant square, it would trigger, as long as it was not adjacent to you at the start of their movement.
EDIT: Opportunity Attacks (DDI) don't trigger if the enemy is using a shift, teleport, or being moved by forced movement. However, specific rules trumps general rules, and a feat is more specific than the general Opportunity Attack rules.
Other way to see this is that the feat is actually an Opportunity Action (DDI), and as such, have its own trigger that do not care at all about Opportunity Attacks, that is only another opportunity action.
In either case, the answer remains the same: The wording on the feat allow you to make the attack as long as the enemy that started the movement non-adjacent to you enter an adjacent square, regardless of how he approached (except Teleporting, that specifically rules out opportunity actions).