Here is a post from @soozievt from 2004 that mentions Unifieds, so they certainly go back that far and farther:
http://talk.collegeconfidential.com/discussion/comment/140224#Comment_140224
My guess would be that they were started in the 1990’s maybe even in the 1980’s. If you are really curious, you can try emailing Peter Sargent at Webster. He is a great guy and will probably respond.
By the way, for fun you can poke around in the thread listed above and see what MT audition life was like 13 years ago. The farthest that I think you can see back in time is this thread: