I managed to get through it without losing anyone on the first try. However, I got lucky.
I kept having shambling corpses get caught at a chokepoint some how; they'd just stand there and do nothing. When roughly half the enemy is not contributing to your demise, things get slightly easier. This was on normal, and about the first time the AI has done something ridiculously boneheaded in my experience (at least with an enemy. Allies on the other hand...)