Russian often reduces unstressed и,я,е, possibly some others, to a short i. Unless you are - talking - slowly - to - foreigners (the turtle-speaker button) and stressing everything, that sentence sounds OK for 'Is he not a PERSON?' (as opposed to 'Is he NOT a person?!' with stressed 'nye').
Possibly, but I wouldn't. Russian doesn't seem to have singular 'they' or any other pronoun that doesn't indicate gender (Shady Arc, who we also hear from on DL, commented on https://russian.stackexchange.com/questions/6899/do-gender-neutral-pronouns-exist-in-russian). But 'это' on its own meaning 'this thing' (as opposed to 'этот/эта/это [m/f/n noun]') doesn't change by gender e.g. the previous sentence DL showed me was 'Это девочка?' - Is this a girl?'.
While it's true that Russian doesn't have articles, that doesn't mean that the concepts which English expresses by different articles are not distinguished in any way at all. Russian just does it trough other means.
This question unambiguously is about his humanity. It can't be interpreted as a question about whether he is any particular person or not. So I don't think that "Isn't he the person" would be the correct translation.
You can't really translate "Isn't he the person?" literally as it is in English. In this case you'd have to substitute "the" with "that" or otherwise rephrase the sentence. "Он не тот человек?", "Это не тот человек?", "Разве он не тот самый человек?", "Не тот ли это человек?"... something like that, depending on context.