"Does anybody know him?"
Translation:Хто-небудь його знає?
No, and I think it's only better. Sounds more polite and not so abrupt. I definitely add "чи" and/or "а" when I speak and the question is not very related to the topic, to smooth it out.
I also say: "Чи хтось знає його?" when I speak. It's more fluid and less 'wordy'.
This sentence with precisely this word order is accepted since 1 year ago. Maybe you made some other typo or mistake?
In general хтось is more like "somebody" and хто-небудь is more like "anybody".
So, "Хтось його знає?" sounds like "Does somebody [here] know him?". While "Хто-небудь його знає?" sounds like "Does anyone know him?". Which can mean really the same as the first sentence. Or can have a wider meaning ("Does anyone at all know him") or a different feeling (e.g. more annoyed).