The classic view of monism and dualism is that they're opposing ideas--that dualism, the believe that reality consists of more than one fundamental substance, is opposed to monism. I've come to a place where I prefer to look at monism as a subset of dualism. But, first....

Monistic world views:

Atheism: All is matter. Consciousness is a product of electrochemical reactions, which are ultimately the result of physical properties. If we crack the unified theory, we may have new perspectives into the true nature of reality.

Buddhism: Monistic, but doesn't really speak to the fundamental substance. Not opposed to scientific discovery, so other than an interconnected, true self, not really all that much different than that atheist world view. Just not so confined to the an individual, wandering mammal.

Hinduism: All is consciousness. Matter exists as our experience of matter. Regardless of whether monistic consciousness is real, there's at least some philosophical truth to be found within this world view.

Dualistic world views:

Christianity/Judaism/Islam: Matter and soul/God/spirit.

So, back on topic... the idea that monism is a subset of dualism. One of the things that brought me here is the dilemma of determinism. It might not seem like a problem until you try to think through it, but in a monistic world bound by cause and effect/change/time, I see no obvious way to escape (in)determinism. So, that leaves us either with a monistic reality with no free will, or some form of dualistic reality.

And, maybe the whole idea of free will is just wishful thinking... or, more accurately, what we were always going to think anyway. But, assuming that we maybe do have free will, how could that be? There would have to be some sort of external force, outside of the deterministic bounds of time and space, that could change the flow of reality. The thing that very well might be what people call "the soul," or "God." We can hardly anthropomorphize something that exists outside of time and space, but that doesn't mean it doesn't exist in some sort of form.

Either that, or what? We're not controlling life--we're experiencing it as it always was and always will be determined. We're along for the ride, so to speak?

But, back to the original point--these ideas aren't contradictory. Minus the clutching at dogma, eastern religion and atheism don't really contradict monotheism. They speak to a subset--the monistic aspect of reality. Whether there's another fundamental substance, or maybe even more, is still a possibility.