Plague Zombies have recently made a come-back in 40k, with Typhus allowing you to turn your cultists into fearless, flesh-eating, monsters, but luckily you have always been able to take them in the Lost and the Damned epic list. They can represent zombies from any of the gods (or none at all) – plague zombies from Nurgle, pain-crazed loonies from Slaanesh, blood lusting Khorne worshippers, or even lobotomized minions of Tzeentch.
In the Lost and the Damned list, the plague zombie formation consists of 3+2D6 (an average of about 10) stands of 10cm move, FF -, CC 6+, 5+ Armour Save infantry for 175pts per formation. Nothing particularly stellar, but these guys are already dead! In addition to the raw stats they also have the Infiltrator, Fearless, and Teleport special rules – meaning that at the beginning of the turn they can appear anywhere on the board. In addition to this they have a note which states that they may only contest, not claim, objectives which drops their utility quite a lot.
In game, your best bet is using this formation either as a last minute objective contestor – drop it on your opponents blitz and deny them the Defend the Flag victory condition – or use them as a roadblock to either block off areas of the board or force the enemy to move out of their zone of control.