The Endpoint software can be set to authenticate to the RBS Server, and then send backups to Google Drive through Google Drive's folder mapping application.

Use the Cloud Service feature. In this case the RBS Endpoints will send their backups to separate Google Drive accounts, one account per Endpoint. Backups will be sent directly from the Endpoint software to Google Drive without passing through the RBS Server. 

The bandwidth used is all on the Endpoint side.

If you want to use a single Google Drive account for all Endpoints, you can set the Endpoint software to send their backups to the RBS Server, and then point the RBS Server's Root Folder at a Google Drive folder. In this case the backups will go FROM the Endpoint software, THROUGH the RBS Server, and be stored on Google Drive.

The bandwidth used is on the Endpoint's uplink and the RBS Server's downlink, AND on the RBS Server's uplink.

We do not know if multiple Endpoints can all log into the same Google Drive account.