Yes, the ghost killed in dreams count for the spell as well. I find it kinda silly too, but that's how it works. We had a long thread about it a couple of years ago I think, and it was not a bug, it was the way it worked.
Harald was an awesome foe, but as I said, a little bit low in MR. He is strong, but vulnerable to Mind hunt+Soul Slay or Vengeance of the dead, specially when casted by a high level astral mage with penetration effects (as Beleren). However, there's no way to build a SC that is completelly undefeatable, all of them have some weakness, even if it's small. Otherwise the game would be a rush to find a SC, and nothing else would matter.
My original plan was killing him with Stellar Cascades spam. In my tests in Single Player against that exact SC, it worked 100% of the times. However, he moved away from my capitol, and Grand Thaumaturgs have map move 1
