It may be impossible to verify if someone is conscious in the same way that I know I am, but we can associate a set of behaviors with an intelligent creature. If we empirically prove that those behaviors emerge from a collection of neural impulses, then it takes a simple assumption (almost a cognitive axiom) that the creature exhibiting those behaviors is conscious, to conclude that emergentism has been empirically verified.
I feel like your position that emergentism is empirically impossible to verify is itself a strong position, and attempts to define a boundary on science when your stated goal is to place doubts on where the boundaries are. Yes it requires a few assumptions, and yes those assumptions are impossible to verify empirically. But then so are the mathematical axioms. We don't go around saying "physics is impossible to empirically verify because mathematical axioms are impossible to prove and are incomplete"