I'm a prisoner here. Darion is getting up there in years and he needs a dedicated physician to look after him. The Khans keep me here for his needs. I'd rather be here for the people in the town above.
Doc Jones works for the New Khans of Vault 15, albeit against his will. Serving as the personal doctor for Darion, he is privy to many of the New Khans' leader's personality disorders and eccentricities. He fell under the service of Darion while on route from Vault City to New Reno to spend his vacation. Jones says that he originally came from NCR. There he trained under the medical staff after realizing he had medical talent. He claims that after he had learned all he could, he traveled to Vault City, but was denied access. He goes on to say that he met Dr. Troy after treating a citizen outside the walls. He was allowed to gain access for medical training, but, upon completion he was captured by Darion. It unclear however, what his relationship with the people of Vault City was before his capture, as few people are known to leave Vault City willingly.
Therefore, one might infer that Doc Jones had misgivings about his work for the people of Vault City, the citizens of the city, and/or the social structure of the city itself. Overall, Jones appears altruistic in nature, caring little if not none at all about wealth or reward, as seen by his wanting to treat the squatters above the vault instead of Darion.