Hello Peter,
In our presentation at OZRI we were using an Enterprise Geodatabase (SQL Server) local on our computers and an Enterprise Geodatabase (SQL Server) on an Amazon cloud server.
From the Enterprise Geodatabase on the Amazon cloud server we created Map/Feature services in ArcGIS Server. These were then consumed via ArcGIS Online to create a webmap which Collector for ArcGIS consumed.
The data was synced between the Enterprise Geodatabase (SQL Server) local on our computers with the Enterprise Geodatabase (SQL Server) on an Amazon cloud server via Geodata services running on the Amazon cloud service using the Distributed Geodatabase tool set in ArcGIS Desktop.
Currently you cannot do this syncing direct from ArcGIS Online to your internal systems you need the data to be hosted in a web service that is accessible to ArcGIS Online.
Regards
Gordon