Jack Ritschel voiced Sc1 Overmind. Eiding was the voice for the Overmind in Sc2.
I'm not sure if Sc1 was really made with the intent of a franchise in mind. Sure, Blizz was riding on the coattails of Wc2 success but like I said, this was a new IP at the time (that initially tried to copy WC2 aesthetics at first) and any up and coming developer is just one bad game away from being confined to the dustbin of history. All the stuff in the manual was fluff (by which I mean it as a term of fact, not a judgement) to promote investment; to craft an illusion. All good fiction is designed to compell and pull you into what is ostensibly "made-up stuff". I'm okay with it just being fluff and living in my mind. I don't need "continuations" which are nothing more than just blatant cash grabs.