There is potential here, but you would need to pick up a few cards to make it effective. In my, admittedly limited, experience, milling an opponent is REALLY hard to pull off as you've essentially tripled your workload (needing to force 60 cards out rather than do 20 damage). The zombie angle is interesting and could be pulled off...
A few cards you're going to want:
Ghostly Flicker - this is SICK when paired with Geralf's Mindcrusher, especially after he's come back in with his undying. Not only would it remove the +1/+1 counter, but that's another 5 cards for them to lose. You could also pair this with Conjurer's Closet as a more consistent way of getting his ETB effect.
You really need more Geralf's Mindcrusher and Undead Alchemist.
Endless Ranks of the Dead - since I'm guessing you're going for casual, and not competitive play, this is a BEAST of a card. With 2x in play you double the number of zombies you're sitting on each upkeep.
Diregraf Captain - you have two in there, and I would say to add two more. He adds an entirely new way to win the game. Not only are all your zombies bigger, but if they do die, you get to do 1 damage to them anyway.
Grimgrin, Corpse-Born - this guy is all sorts of fun in this sort of a scenario. You sack the mindcrusher to him, it gets a counter, he gets a counter, you flicker the mindcrusher and repeat.
Trepanation Blade - not one that really gets considered for most mill decks, but this has the potential to be a monster. Equip one of your zombies (who really cares whether it survives or not) and swing away. It can cause someone to drop a LOT in a single swing.
I would definitely work to get another Mind Sculpt and if possible Jace, Memory Adept (I know PWs are hard to come by, but man, he puts a clock on the game the minute you play him down with his 0 ability).
A few added thoughts - I would definitely say to dump Zombie Goliath - whether you put in Walking Corpse or Diregraf Ghoul either one is more likely to see the battlefield and be influential, especially in the early game.
I can actually see where your instants will almost all be worthwhile here (who would've thought Vile Rebirth could work for someone).
Personally, I'm a fan of Moan of the Unhallowed far more than Reap the Seagraf (you get two zombies for one more and then can flash it back to get two more zombies for only two more mana than flashing back Reap - so to do it by cost that's 11 mana for four zombies, or just four mana for two zombies, compared to eight mana for two zombies, or three for just one). I would try to pick that up to 3-4x there.
Mystic Retrieval really doesn't help you here. You can't flash it back, so it's just four to get one spell back, which you could easily do with Archaeomancer while also getting a chump blocker. But more so to the point, what do you envision needing to pull back out of the graveyard?
Demonmail Hauberk - Why is this in here? If you're looking to power up some creatures, why not use Tricks of the Trade or Mark of the Vampire? Neither has seen much play in constructed, but they're game winners in sealed format competition. Make a zombie unblockable or give it lifelink? Sure. If you have the Alchemist out and hit it with Tricks of the Trade that's a guaranteed six cards they're losing each turn.
Curse of Oblivion - this doesn't really do you much good. If you want to exile their graveyard, you could hit that for free with Tormod's Crypt - but by my estimation you want them to have their graveyard so you can cast Vile Rebirth.
Anyway, that's a lot of food for thought... I hope it helps (on a side note if you post those other two decks on the forums here I can give you help on those as well - in addition to the rest of the community, I promise they won't bite... well... not hard at least).