Yoy misunderstand. NTSC and PAL has nothing to do with the DVD-zones... both video-systemes may be present in all zones. They have been decided on a per-country bases, after what analoge TV-system they once decided to use.
But yes, it should be fine to let one drive be set to Zone 1 (USA) and the other to another Zone (like Europe or Japan).
The Zone will decide if you can play the DVD at all. If you can play it, the video-signal may be coded in either NYSC or PAL. Then it depends on your video-card and monitor if they can actually use this signal in an useful way. As you're using a computer and not a TV directly, the computer (software) may handle both, and convert it into something your screen-card and monitor understands anyway.