a colour monitor is handy. now honnestly. when you are comping in nuke you more or less never look at the stereoscopic result.
the workflow in nuke let you work on one eye and if your disparity map works fine and you have converted and adjusted all your masks,
cc and keys to the other eye then you watch it in stereoscopic, but at this point you are sure that the colours are fine. so the only thing that you are going to check is if the stereoscopic effect runs well and to check this anaglyph is absolutely ok and that works with every colour monitor. so if we are talking about a workstation there is no need for a 3d monitor. if you need a presentation monitor for clients to watch the final result, thats another story.
best
otaku