Uh, no, Rob Paulsen was voicing The Smurfs, G.I. Joe, and the Snorks before that show. Ed Gilbert did some voices on Transformers, and Tony Jay had been doing voice work for radio commercials in the 70s. Though to be fair, I do believe that Greatest Adventure was his first cartoon work (still not his first voice work though).
I kinda knew that. I've just noticed that after the show, they moved onto titles they made them bigger in voice acting.