Yeah, settled obviously doesn't dispense the fact that the Kings just took on a dude who beats on women. Yuck.
I'm not condoning any of this but the charges were dismissed, first of all.
Secondly, the league had also decided that he will not be disciplined further for it.
Last but probably most importantly, mainly for your concern listed in your comment, he is in a measly 2 year / $2,416,291 contract with the Toronto Raptors, including $2,416,291 guaranteed so it won't be a huge loss IF he gets in trouble for whatever reasons and we have to cut ties with him.
So just like most of the trades McNair has made, it's low risk with potentially high reward situation.