My Range Rover has similar "over-pressure" vent(s), visible fron the outside at the base of the rear side pillars. Without some form of vents (and I've known someone whom this has happened to, even with vents), the pressure of shutting the rear hatch (on a newer Rangie), the rear window blew out; shattered.

Surely they have more to do with fresh air circulation as part of the HVAC. Of the two Rangie vents, only one is functional (right side), and it has a rubber flap, presumably to allow air to move from the interior cabin to the outside, but flapped seled for air/water to move from outside to in.