I found these two quotes.
There might be more but this is enough to show that adoption is a real thing.
"I was raised in that house," she said "with love, though I was only slave, and Samos was to me almost as a father might have been. I was permitted to speak to, and learn from, scribes and singers, and merchants and travelers. I had friends among other girls in the house, who were also much free, though not as free as I. We had the freedom of the city, though guards would accompany us to protect us."
Raiders of Gor    Book 6    Page 292
At the age of twelve, Ute had been purchased by a leather worker, who dwelt on the exchange island, administered by the Merchants, of Teletus. He, and his companion, had cared for her, and had freed her. They had adopted her as their daughter, and had seen that she was trained well in the work of the leather workers, that caste which, under any circumstances, had been hers by right of birth.
Captive of Gor    Book 7    Page 233
