They are not suppose to have blood, hence why Artery/Twist/etc does not work on them. However Hurl still causes bleeding, which by the logic should not. Also, not sure if poison should affect them either with no blood to poison.

A shadowed Nightwalker shivers and suffers.
A shadowed Nightwalker's poison EVISCERATES it!
A shadowed Nightwalker continues to bleed from its wounds.
A shadowed Nightwalker's bleeding EVISCERATES it!