There are actually two forms of non-dualism: materalism and idealism. One is that everything lives in the material world and the other is that everything lives within the world of thought. For various reasons, materialism is the only non-dualism scientists give credence to.

Skinner's a materialist, too. He may reject emotions, thoughts, and free will as fiction, but that's because there was, at his time, no scientific evidence for them. Neurology may have changed that, and so in fact may have continued behavioral research. (I suspect there are behavioral studies which would have shown a consistent "internal state" factor to animal behavior, for instance.)