The idea of video taping rehearsals is fine, and many LDs I know use them to cue the show without the actors present (high-tech dry-tech?), but I'm not sure how useful a bird's eye view is going to be. Most actors and director's don't understand "plan view" so you'd have to interpret what's on the video. We're not talking Busby Berkely here, right? When I used to stage manage, I would always base blocking notes on landmarks "crosses from 2' US of sofa to door DSR."
I do know a director who swore by pre-blocking his scenes on a 1/4"
ground plan using pennies, which he said were the ideal size of an actor. But since we're most likely talking about
proscenium theatre here, the picture the audience sees is way more important than what the grid sees. If you're using the notes to put in a replacement cast member, you're not going to be "directing" from a bird's eye view, most likely you're going to be in the
house.
Hope this helps. Just my 2¢.