That's not a vent (invoke Death Star reference) it's part of the interior alarm system. If you block it, the car alarm won't detect someone breaking the window and climbing inside, so do so at your own risk.
(Clever system - it sends periodic ultrasonic pulses through the cabin, and detects the change. My car has two - looks like VW has changed the design to only have one nowadays.)
I really think they are vents, I have watched many videos of Dashcam installs on Golf 7/7.5's
Some videos dismantle the plastic housing behind rearview mirror to hide cables and it looks as if it's an empty area. Maybe for the Road sign recognition system (camera) available as an option. But it's defiantly not part of the alarm wouldn't make sense in its position and the manual only show the other location for the internal alarm sensors.
I have yet to route cables through the headliner and down the A-Pillar to fuse box. I want to expose the top of A-Pillar and hopefully feed cables behind airbags (I've seen it done on youtube). Although many USA Professional installers feed it into the gaps over the airbags and say it doesn't effect airbag deployment. I's feel better if it was behind.
I'll keep you updated but might be a fews days before I get back to it.
Very helpful and let me know how you get on. I actually have the roadsign camera, and dynamic headlight option so there is a camera up there somewhere but not 100% where it is. The photos at the start of the thread are my car so it looks like the camera is not behind the vents
Only issue was getting cables behind airbag in a-pillar, I tried popping off top of a-pillar but felt I was going to snap it and then decided to pull the top of it away and wedge some spacers in. Then from the door rubber side could see Airbag and cables. I very simply used a cable tie to push behind airbag and cables and came out at the windscreen. Feeding cables down to fuse box and back to boot lid very simple. Covers on boot lid just removed easily with fingers.Then used very heavy cable to feed cable through rubber between car and boot lid.
I am having a new windscreen today on mine as they have made a pigs ear out of repairing a chip. It has had to go to Chester for this to be done because they will need to realign the camera on the screen. I have asked them about the vents from the original question above so I will see what they say about them when I pick it up later on .