You are correct, you can tap the sync off the S-Video straight in the G-Con connector and pin 1 is ground.
The driver does NOT have a thirty day limit, that's just for the dev kit.
As for me, I downloaded the driver earlier tonight and have the gun registered with windows (note you have to use the batch file installer and I for some reason I had to modify it under WinXP to get it to install correctly). I had hoped it was possible to use the composite video out on the ArcadeVGA to drive the GCON but the drivers don't seem to allow it to be enabled. I should have know this as the modes are not standard TV resolutions. This means I'll need to create a special cable to extract the SYNC's. Thankfully the ArcadeVGA always uses negative going SYNC pulses so it would be easy if I had two small caps and a spare VGA cable. None of the buttons work yet but that could be because the gun is not detecting a sync input - let you know how I get on.
PS, I am using a D9200 monitor - have to see what happens with that!