From FS1 - the actual Descent: FreeSpace game? Yes, it's possible, but I don't think anyone ever actually made multiplayer co-op missions. There are, however, multiplayer co-op missions for the Silent Threat campaign.
Now, for FSPort, that's a different story. Parias made a pretty good start on this a few years ago:
https://www.hard-light.net/forums/index.php?topic=88385.0Sadly Parias seems to have disappeared, and his ported co-op campaign is still in beta, but I think with a bit of polishing and the latest multiplayer test builds, this may be just what you're looking for.
