Do reverse bear traps kill survivors past the exit gate if it has not been activated?
When a bear trap is active and you try to leave it kills you but does it still kill you if it's not active?
No.
Once the exit gates are powered, the only thing putting a trap on someone does is give you points.
This was a change implemented alongside the Endgame Collapse; prior to Endgame Collapse being added, traps would automatically activate if they were put on after the gates were powered.