Your assumptions are correct overall, but OTG can be a micro or a mini usb port. OTG can work as host or slave and should be transparent in function. For instance, I can connect my terrabyte USB backup drive to the OTG port on my tablet without any drama. I can also connect a USB to ethernet adapter without a problem.
It does however depend on the implementation and supporting drivers supplied by the manufacturer. I have seen 1 device that is OTG, but the supplied charger is 9v. It does charge through the OTG port, but at a much lower rate.
--- Jem