Quote Originally Posted by The Bushranger View Post
'Good' and 'Evil' actually don't concern Nabu, actually, I believe. He is a Lord of Order, not a Lord of Good.

It just so happens that Order and Good usally coincide (and Chaos/Evil likewise, see also: Klarion).
Well he's never been shown in the comics to ever aid an evil act just to maintain order so you could say the morality of a host helps in that. which is why such beings need mortal hosts.