I don't see a stealth skill as a bad thing if done properly, and makes sense in the context of the game mechanics (Where skills primarily determine the process rather than the action).
Stealth, for the most part, would determine the use of obstacles in keeping hidden from monsters the character is aware of, and keeping quiet when moving over noisy surfaces, such as gravel or foliage. The player still determines where to hide, where to go, whether to actively sneak, etc, but the character does the small things. Primarily it'd determine how fast you go when sneaking, how far behind an obstacle you can be and remain hidden, and the likelihood of enemies seeing you in certain situations (Such as hiding in an item, like a bush or cupboard). Hiding in plain sight should be impossible solely by using the stealth skill, unless you can turn invisible or something.
Of course, in order to have proper stealth gameplay the game would need the enemies to have a cone of vision and facing. I'm not sure how I feel about that.
Alternatively, allow the player to be very involved in stealth, and forget the skill altogether or have it determine the amount of noise you make when performing certain actions. This would require the ability to crouch, keep low while moving, go prone, and crawl.
I also had another idea while thinking about alternative ways to avoid zombies. You know how you can distract a dog that's tracking you by touching objects you pass by, like trees? It'd be fun to have zombies do the same thing. Obviously useless if they can hear you or see you, but it might give you a few precious seconds to get away from the horde.