Yes. RMII is 8 signals for the data. 2 are used for controlling the PHY, and the other 2 are reset and interrupt.
We're currently not using the interrupt pin, and probably never will. But it also functions as a powerdown pin when not configured for interrupts.
The RXER pin probably isn't really needed. When the PHY detects errors it transmits invalid symbols which the MAC uses to know the data was corrupt.