We don't usually use "dark" for name,
but we use "sky" a lot. "하늘"
I think 하늘 is very pretty name.
And I hardly ever heard "night" "밤" for Korean name. I've only seen that name on the internet webtoon.
(If you are interested in webtoon, I highly recommend that webtoon named 신의 탑. I heard naver webtoon has English version app too.)
Anyway you can use 밤 as well, but because people are not familiar with that name, if you introduced yourself, people could ask "Sorry, what is your name again?" like this.
But for me, 밤 could be a cute name. The pronounciaition is very cute.