Its hard to find anything in nightmare that doesn't suffer from instant death at the hands of the AI. I don't know if the dagger rogue is any worse then say, a mage or archer that runs into melee range, or a 2-hander trying to play tank.
There are some skills in the game which suck for the player, but change the game in the hands of the AI. Take a look at parry. I will never get that skill to do anything other then suck, however, set it to preferred for the AI and watch as it effortlessly deflects deadly attacks with ease.
I set up cole AI with parry, stealth, and flank attack set to perferred, and he seems to have about as good survivability as any other AI class save the tank. He is set to guard the tank. Its the only time I use guard for the AI. He only attacks enemies who are attacking the tank which works out well. I've seen the AI carefully set up for flanks from stealth, deal durst DPS, then fall right back into stealth.haven't tested evade, but if the AI can make good use of that skill too then DW rogues might just make it in nightmare decently.
EDIT: oh yeah, and don't forget the threat reduction skill from flank. That skill is vital.