Is ULPI the only protocol for interfacing with USB devices?
ULPI specifications are limited to USB 2.0 data rates only, 480 Mbps maximum. There is no USB 3.x PHYs that can possibly use ULPI for susper-speed rates. The high-bandwidth (5000 Mbps and 10000 MBbps) link that is used in USB Super-Speed PHYs is called "PIPE3" interface.

However, since the USB 3.x provides backward compatibility simply by running the new super-speed hardware in parallel with legacy USB2 hardware, a USB 3.x PHY must support both channels, Super-Speed, and the legacy USB2.0 signaling, and therefore must use BOTH interfaces, PIPE3 and ULPI, see this Texas Instruments block diagram,



AFAIK, all designs I saw (Cadence, Synopsis, SiBridge, etc.), all are using separate channel (UTMI+ or ULPI) for legacy USB 2.0 support.