I am able to scan b&w negatives and open them in NX2 when they are scanned as 24- or 48-bit RGB and saved as JPGs.
I can then save the image from NX2 as a tif and reopen it in NX2. So much for ease of use, but it is possible to start with a film scan.
I am not an NX2 user, but it looks like it's primarily a raw converter, so Nikon expects you to start with a nef or nrw from one of their digital cameras.
Just to be clear: scan your negatives as Media=B/W negative, *not* Color negative.