The concept is actually more commonly called "human computation" (which includes stuff like digitizing books using CAPTCHAs).

It has academic journals/conferences under that name: http://hcjournal.org/ojs/index.php?journal=jhc

Not sure if MT works when some specific knowledge is needed (I think their employees know or have quick ways to find out the correct matching dress given a photo)

Yes perhaps for training the AI.