The USB-8451 does not use NI-DAQmx; it uses a separate driver and API (NI-845x; the latest version is 2.0).
It's compatible in the sense that you could have both NI-DAQmx and NI-845x installed at the same time, since they're two independent pieces of software. It's not compatible in the sense that you can't use the USB-8451 with NI-DAQmx APIs.
