I think that all of the original Zombie Master zombies should be put back into the game. The only change, is that you should balance them. You should take out all of the zombies in v1.2e (Blob, Zombie, etc.)
Mentioned in one of the posts above me, a zombie dog. Instead of calling it a zombie dog, hellhound sounds a lot better. A hellhound is fast, a good strategist (works with other dogs), and can deal damage fast (it hits fast but doesn't do much damage per hit). The disadvantage is that they are very easy to kill. I am not sure how much they should cost but they should be sort of cheap.
Abomination (Name can be changed)
Once again, this was mentioned in one of the posts above me, except I think it was named Brute. Abomination to me seems a lot better of a name. Abominations should be giant, be able to deal tons of damage very fast (it hits slow but does a lot of damage per hit), have lots of health, and be able to have a burst of speed once a survivor is targeted (just like the immolator). During that burst of speed, any zombie in its way will be destroyed. The zombie master has no way of stopping it once it has found a target. The disadvantages is that they are expensive and slow (when a survivor isn't targeted). I think the Abomination will need a lot of testing before it is balanced.
Summary: I don't think too much zombies need to be added but the old ones need to be for sure. One thing that needs to be changed about the older zombies is how much they cost. Nobody likes hulk spam or banshee spam. There is a reason both of those are possible. They are to cheap!