の can be a placeholder for many different things, including people and abstract concepts. In your sample sentence ("Who can't see?" or "Who is blind?") it refers to a person, but in other contexts it would refer to something else.
Note that の is often used to serve a similar function as こと, although you cannot use こと as a placeholder for a person. In other words, 「目が見えないことは誰ですか」 would be grammatically incorrect. However, you could say both 「目が見えないのは難しいですか」 and 「目が見えないことは難しいですか」 ("Is it hard to be blind?"), with the difference being that the former emphasizes personal experience and the latter emphasizes the abstract concept of being unable to see.
Anyway, to answer your question directly, 「目が見えないのは誰ですか」 is grammatically correct and sounds perfectly fine to me if you're trying to pick someone out of a crowd. I'm not aware of any particular rule against using の as a placeholder for a person. You could always use 「目が見えない方は誰ですか」 if you want to be more polite, though.