Can I use the MAX3420E in a bus-powered peripheral?

Yes. In a bus-powered application, a 3.3V voltage regulator is connected to the USB connector's VBUS pin. Whenever the peripheral is plugged into the USB, the chip and the SPI master driving it are powered. There is no need to connect the MAX3420E's VBCOMP pin to VBUS. In this case, the VBCOMP input can be used as an extra general-purpose input. Care must be taken to ensure that input signals to this pin meet the threshold requirements noted in the MAX3420E Electrical Characteristics table.