Undying Hate triggers before deployment. My knee-jerk reaction to this timing is that it turns a powerful upgrade into a mediocre one. If your opponent knows before deployment which of his units has Mark of Vengeance, he can deploy in such a way that your Wraiths may never get to attack that unit. Of course, you could always save your Wraiths for last, too.
But the more I thought about it, the more I started wondering if there weren't some way to leverage Mark of Vengeance during deployment. Could yoy use it to manipulate your opponent's deployment? If so, that would be awesome. But then I remember that it's just upgrading one die to a white die, and usually I think you're just trading blue out for white. That really isn't threatening enough to let it affect your deployment, is it?
EDIT: I also find the timing unfortunate because Kethra can respond after deployment by putting Unnatural Growths on her allies that received Mark of Vengeance. The Wraiths can go ahead and attack with their white die, but they're going to lose a figure before they even get to roll.
Edited by Budgernaut