Two devices using different drivers and different VID/PID combination's but the same firmware can co-exist and operate normally on the same host pc.
Two devices using different drivers with the same firmware and VID/PID combination can co-exist and operate normally on the same host pc.
The driver to be loaded for each device is dependent on the USB port attached to the device. The same firmware can be used on different USB ports on the host pc. You can load each port of the device with a different driver by modifying the INF file.