“As a theory of mind (which it is not always), emergentism differs from idealism, eliminative materialism, identity theories, neutral monism, panpsychism, and substance dualism, whilst being closely associated with property dualism. ” (WP)
As a theory exclusively of the mind, I can see that emergentism has implications like property dualism, but not as a theory that treats the brain just as a very complex system with similar issues to other complex systems.
Reducing to “physical properties” is not necessarily the same as to “the physical properties of the ingredients”. I would have thought physicalists think mental properties can be reduced to physical properties, but reductionists identify these with the physical properties of the ingredients. I suppose one way of looking at it is that when you say “in principle” the principles you refer to are physical principles, whereas when emergentists see obstacles as present “in principle” when certain kinds of complexity are present they are more properly described as mathematical principles.
Mental events can certainly be reduced to physical events, but I would take mental properties to be the properties of the set of all possible such events, and the possibility of connecting these to the properties of the brain’s ingredients even in principle is certainly not self-evident.