On the industrial side of Chernogorsk and on the west of Prig, there is no zombies roaming around those parts. I was playing on a vanilla server too, DayZ Underground. It wasn't until I reached the city part of Cherno, where zombies appeared. (No zombies even in the the cherno military camp)

This may have been because I logged in to the train station in Prig, looted a few houses, and then went to Cherno, but I don't believe so.