I don't think it is Inarius because:
1) Yes, Inarius was the Prophet, but saving the lives of someone, in secret, just doesn't seem like his thing. I don't think he'd be concerned enough with their lives.
2) If it is Inarius, it would have to be before the Sin Wars, cause since tSW, he's been stuck in Hell.
3) All of Inarius's followers were killed by Lillith. Therefore, how would any of the Angels in HH alive at the time of D3 know anything about what Inarius did?
4) If it was Inarius, I think he would have said more about his church, and not been secretive about his origins.
5) Her master who was summoning demons was a Vizjerei. I don't believe they were really around until after the Sin Wars (why would the Triune or the Temple of Light allow demon worships to exists outside their own structures?)
I think it could be Malthael or Itherael. Both are known for being able to predict things incredibly well, and Malthael is said to be able to counter blows with the slightest of force - as the enchantress was clearly necassary to beat the early part of Act 2, I would the actions of the prophet count. The problem with it being Itherael is that, I believe, Auriel and Itherael said they did not know anything about the prophet. Of course, it's always possible Itherael was just lying.