Trying to Spawn some Mobs from a Mob Spawner i discovered that the next Mobs do not Spawn if on a Mob Spawner:
Cow, Pig, Sheep, Chicken, Zombie Horse, Skeleton Horse, Polar Bear, Donkey, Wolf, Slime Squid, Llama, Bat, Ocelot, Horse, Mushroom Cow and Mule.
This was Tested on a 5x5 Zone with the Spawner in the Middle.
Make sure there's grass blocks nearby for them to spawn on.