@chibiacer I originally thought something similar when Hikari was introduced. However, she and the other black hair / black eyed test subjects of the kingdom lack the otherworld identifier that Sora has when he appraises himself and others.
Much more likely they are descended from other summoned individuals, possibly those similar to Sore who lacked "beneficial" skills or had out-lived their usefulness. Hence Surmire never understanding what parents were, having likely been separated from her mother at brith, who was simply being used as breeding stock...boy, and you guys thought the author's slavery fetish was bad.