Does a Gen 4 have the rear cargo area vents that mice can get in?

Yes I assume you mean the pressure vents. All cars I know of have them. They let the pressure out when you close the doors.

 

I'd suspect the vents are the same, kind of like cheap dryer vents, a roughly square grill with a flap. Take a look?

I'm not sure they're "perfect" entry points; the cabin air intake is more common entry point. But yeah, it's a possibility. I've meshed the cabin air intake (on our 3rd gen); have been meaning to do those rear vents. Main issue is figuring out how to do it, it's kind of an awkward/bulky vent, clean/effective mesh install will be tricky I think.