I'm not familiar with using one in that fashion since all of the Nieman monitors I've bought have gone into dedicated machines, but it wouldn't be any different than using any arcade monitor with a PC, a topic that's covered very well here.
I can tell you that the tri-mode monitors are NOT digital (which I prefer to see in a dedicated machine). The drawback to non-digital, multi-mode monitors with a mame machine/PC application is that the monitor won't retain adjustment settings across different resolutions. Switching between CGA and EGA, for example, will likely require adjustments to the image size and position. The solution is to use the monitor in only one mode, as you would with a standard arcade monitor in a mame machine.
Rick is now supplying digital monitors with OSD features (on screen adjustment menu), however they only support VGA and higher, so these would be akin to using a regular PC monitor.
D