Na, Ner’zhul was just an old orc who made a bad deal and ended up paying for it. The Jailer - aka Zovaal - is an Eternal One who predates that orc and just about everything and everyone we know.
I think that he either ruled a domain which we haven’t seen yet, or acted as the Arbiter. The blasted pedestal in Oribos was probably where he stood and where he was taken down, as it were. Why? Well, I think he rebelled. In the Collectors Edition Art book it says:
“…and so it was decreed that he would be condemned to the Maw where he would forever be its Jailer…”
So he didn’t start there, he was sent there for committing something that the powers of the Shadowlands (or somewhere else??) considered to be so heinous that an apt punishment was to spend an eternity in the Maw.