This PvZ replay has the folllowing:
- Proxy in the exact location you describe, behind 2 gateways.
- Successful scout with a Drone, no gateways or cores so immediately looks for the proxy.
He does this in both Tzenes spot (in vision of his drone) and your spot. - Successful scout with an Overlord, nothing in Tzenes spot nor gateways after the Drone leaves.
- The Zealots, Stalkers and Proxy being countered by Zerglings and Roaches.
- This is followed by an expand by Zerg and a series of pushes by both players.
Although Zerg didn't win in the end, I consider he countered the Proxy fine and messed up later.
If you want, just ask and we can try to figure out what went wrong later...
I think that this would be similar for Terran (MM) and Protoss to counter with the same scouting.