I recently setup Google Assistant Relay v2 and was also wondering how this would interact with SmartThings and have built a smartapp to handle POSTing the JSON to the Google Assistant Relay server to get notifications in the event of any of my devices changing state.
Google Assistant Relay Notifications SmartApp
https://github.com/braytonstafford/google-assistant-relay
I’d love to get @ghesp’s feedback on this as well