Immortal soul is not sufficient. It must be an immortal human soul. The Christian economy of salvation is for human beings only. If there are non-human intelligent lifeforms out there, they are neither in need of, nor entitled to, the Christian economy. Unless they were humans enslaved and resettled by the Goa’uld, in which case these “aliens” would indeed be entitled to baptism. I would also argue that Spock would also be eligible for baptism (he is half human), but his father Sarek would not. Worf is not entitled to baptism, but his son Alexander is.
My basis for this is simple, and this is something that goes to the core of the earliest Christological debates: God became human. He did not merely become material, but he took on a full human nature, with a fully created human soul, a real human body, and rational human mind. Alongside this is the principle of “what was not assumed was not redeemed.”