No, in this case u can say 他的性格很黑暗。他是个邪恶的人。U can't use 暗 to mean someone is evil, even though 暗 mean their personality is evil somewhere.

I hardly use this word when I discribe people's personality.I use quite person. Because this word is rude.

Actually,you can say he is a black man referring to his black skin. I'm to you can say he is dark,referring to his personality. They are like 皮肤暗沉 And 内心阴暗。

I never heard people describe a person with 暗，it could be if more and more people using this way in the future.

I have never heard people use 暗 to describe a person. We do use the opposite, 個性開朗/个性开朗 to refer to someone with a bright, happy disposition. The natural antonym for 开朗 is 阴沉, and when you call someone 个性阴沉, you mean that person has an evil, dark, and conniving/manipulative personality. If you say 那个人很暗, I would think "hmm? Does it mean that person is dark-skinned?" (Even though the proper way to say that is 那个人皮肤很黝黑）