I've kept them seperate and use them as a stand alone deck. Haven't heard an official word on it though. Way I figure it, they didn't add new cards for runners, fatties, or abominations so for general play I'll end up burning through walkers quick if I added them in. Then the walkers would run out and would start getting tons of extra turns. I have used the deck though in a couple games, I have to admit it was a bit rougher than I thought it would. Three of the four survivors died, the last one managed to get the last objective right as the walkers ran out (right before the zombies would have gotten three draws with no walkers left and a massive horde a room away).