If you define a "proper" animal as most people would, those with anything resembling human traits, then they are surely all non-human persons. I don't see why a subclade of artiodactyls became special. At Quistacocha someone was gushing how human the river dolphin was because he was masturbating with a blanket in public, not realising pigs will do the same. And even if higher odontocetes with complex societies are especially human-like, more basally diverging species like river dolphins won't be. Even PETA got in on the act of mocking dophin-ists once, because the preference for certain species humans find anthropomorphic is anthropocentric in itself, and detracts from issues on one's doorstep.
Its not that they don't have "human" traits or "personhood", its just that the bits that matter most (like pain perception) are far more widespread in the animal kingdom, that laws being written from human perspectives can at most treat animals as we do small children or the mentally impaired, and that the animals might not benefit 100% from human rights. With small and manageable cetaceans in decline the misplaced concern for them is starting to work against them, maybe.
However, there are dolphinaria in Thailand and nearby countries: yes, local captive populations would be possible.