I just finished with ZG on my MMMMP group and here's how I did it. I would only pull about 2 groups max. The only mobs you have to worry about silencing are the Shadowcasters, the Blooddrinkers and Witchdoctors will pull like normal. Utilize LoS when necessary but you shouldn't need to very much. Also, be ready to move your group when the WD's drop their lava spout totems, the AoE damage can stack pretty quickly from them. And finally, when you get to the GY, open about 4-5 graves at a time, try and count how many zombies you get and stop when you see 5-6 zombies. Slow and steady wins the race.