RS-422 is a physical layer whereas VISA deals with the software communication / UART layer. As long as the RS-422 adapter appears as a standard com port, VISA should have no problems communicating with the port. However, some additional features (such as transceiver control) are only supported for NI's 485 (422) serial products. If you do not have a RS-422 card, you can either purchase a RS-232 to RS-485 external adapter, or go with a RS-485/422 plug-in or ethernet solution which National Instruments offers with isolated and non-isolated options.
