Have a Raspberry Pi 3 Model B USB OTG port?
No. The chip is capable of handling an OTG port, although there is no software for that, that I know of.
The model A and A+ have the USB port of the chip routed to a connector. Officially the wrong connector for OTG, but the signals are there.
The pi zero has the signals routed to a proper OTG connector.
But, as I said: There is no software that I know of that allows you to use the raspberry pi as an USB slave device.
