Thanks for the tip to this app. I just downloaded it out of curiosity, and did a test by turning off the N7's wi-fi and clearing the app's data and cache. As you and I suspected, it leaves you with a mapless white background, on which you can place your parking pin.
It works without wi-fi, and it works without downloaded maps. Of course, without a satellite map view (the most useful, IMHO), it won't show you the buildings you'll have to walk around to get to your car.