Technically skeletons and zombies can be ordered to imbibe fluids (in the case of skeletons the fluid would flow over the bones), so: can skeletons or zombies can use and benefit from potions?
The general rules for potions only say this on the subject:
A creature must be able to swallow a potion or smear on an oil. Because of this, incorporeal creatures cannot use potions or oils. Any corporeal creature can imbibe a potion or use an oil.
So it seems that the answer is Yes, they can.
You can argue that some corporeal but mouthless creatures won't be able to benefit from a potion - and this sounds like a sensible houserule...
The necromancy spell Deathwine has a reference to undead drinking potions:
In addition, any undead creature (or other creature healed by negative energy) that drinks a potion affected by deathwine is healed of 1d8 points of damage.
It seems to me that if any rule in the canonical rule set refers to a specific action then the rule set explicitly condones that action. Therefore undead are allowed to drink potions, and because it refers to undead generally rather than specifying types of undead, undead are generally allowed to drink potions unless exceptions are made elsewhere in the rule set.
The SRD says
A potion is a magic liquid that produces its effect when imbibed. Magic oils are similar to potions, except that oils are applied externally rather than imbibed
Since all that is required is imbibing and not digestion, and they apply immediately upon imbibing. then undead can use them.
Furthermore, even if your QM rules that that they can't, you can just point them at oils. Oils use the craft potion feat, can contain any spell below level 3 (just like potion), and are triggered by rubbing them on something instead of imbibing. I doubt anyone would argue that you cannot rub an oil on a skeleton.
The difference between imbibing and digesting is the problem. What must be assumed in many cases is a zombie is both corporal and incorporal. Sometimes the skeletons, adventures run across have been ordered to scatter their bones into piles as traps. Which pull themselves back together when their orders are triggered. If the potion effects bones I would say yes, for skeleton. Zombies are often cast from the same spell so assume that zombie are both. In this case I would assume any oil or potion that would affect leather. Next problem if a potion requires a choice this choice would require addition to total orders. I don't want you to miss understand because once the potion is digested its magic is spread via the very non corporeal magic.