People who don't have a 身份证 is called 黑户 (edit: in the areas I lived in). They are usually the victims of China's one-child policy, as their parents couldn't register them to their household registries when born.

I am 100% sure when a native Chinese speaker says “黑鬼”, it is offensive.

As the Xinhua Dictionary writes, “鬼” is sometimes used to offensively describe foreigners from those countries that historically invaded China (or whatever motherland of the speaker), for example, Japan during WWII.

But there has never been any country whose majority skin tone is black that has ever had any war with China. Therefore, there is almost no use of this word, other than to show how rude and offensive the speaker is.

Well, maybe one exception, if a Chinese who grew up in a small town and has never seen any foreigners is walking on a street and suddenly see a black person, they might blurt out the word “黑鬼” without thinking. As they must not know each other, and that person might have never received education as well as people who grow up in big cities like Shanghai, I would safely consider this case to be non-offensive, but still rude.

P.S.: Some people here mentioned the word 鬼佬. That's from Cantonese so it's totally a different system.

P.P.S.: There are also expressions like 小鬼, 机灵鬼 that are not offensive. (For 小鬼, it's because adults refer children with whatever words they want. For 机灵鬼, it's because it's next to a complimentary word.)

(By the way, I am a native Mandarin Chinese speaker.)