I was happy to see that in the latest ArcGIS Online update that we can use our own geocoding services. I was able without issue to add one of our services that is on a public facing server. However, it would not accept URL's for the geocoding services on our internal server. Should this be possible? They are 10.1 services.
In this release, we check to make sure the Geocode service is publicly accessible. So Geocoding Services behind the firewall will not work when added through the UI.