Star Trek Encyclopedia says the race that created Armus was native to Vagra II. So that rules out the Founders too, if it's to be believed. Maybe it was the metrons. With their immense power, they could be said to be "titans", and they seem to be pretty do gooder-ish. Well, maybe a little arrogant, but that's about it.
Ah, the race that created Armus was native to that planet, but that doesn't mean that Armus was! Perhaps Armus was one of the hundred, came across the Metrons on that world, and they discarded all their evilness and negativity onto him.
I can't think of anything canon that would contradict this idea, with the possible exception that Laas could travel through space, so if Armus was a changeling as well, why couldn't he do it. But then, it's entirely possible that whatever change happened to him left him unable to travel through space.
A very interesting idea.