UDC

There is a USB client on handheld Vita devices. It uses a proprietary multi-connector on the OLED (PCH-1XXX) units and a micro-USB on the LCD (PCH-2XXX) units.

PCH-1XXX Pinout


Because of the existence of the USB ethernet adaptor, that means there exists a way to use the port in host mode probably through USB OTG or something similar.

Teardown of Vita OLED dock here.

PCH-2XXX Pinout
Port is a standard micro-USB Type B. USB OTG is also supported in hardware and software, as there is an Ethernet adaptor containing a micro-USB 2.0 type B connector as well (there exists a rare PTEL-20xx Testkit Ethernet Adapter: https://i.ibb.co/HDNHNDx/image0.jpg)

The "CBPS" also managed to get USB OTG working and was able to mount a USB drive via VitaShell.