This 7 Days to Die mod is Guppycur’s contribution to the Zombie part of the Creature Pack, available here separately. These do NOT require sdx/dmt to run (Thanks Xyth!). Just install the mod like usual.
You will need to populate the entitygroups with them to see them in wandering, sleepers and hordes, but he is including an xpath for biome spawns.
Technically 3 zombies, but there are 3 variants of 2 of them, so 3×2+1 = 7 new zombies.
The forum topic of the mod is here.