Ah, okay, TIL!

I can say that the backseat cover I use (this one) does not cover that vent. But we use the side flaps in the upright position, hanging the provided straps through the rear ohshit handles, rather than facing downward. I actually wanted this feature, otherwise my 50lbs dog would absolutely obliterate the interior door panel.

It makes getting the dog in and out a tad more of a pain, but it's worth it to me to have that protection.

With the side flaps up, there is no covering of the seat vents.