The voltage monitor does not eliminate the need of a voltage supervisor circuit to ensure that the device is held in reset when the voltage supplies are out of range.
The voltage monitor only monitors the core supply (VCC) and the I/O supply (VCCIO). The other supplies are not monitored by the VMON. For example, if the VCCAD or VCCP are supplied from a source different from that for VCCIO, then there is no internal voltage monitor for the VCCAD and VCCP supplies.