Right, you don't need a metabolism to use a potion, you just need the ability to internalize the fluid in some way. So a zombie or vampire can drink a potion just fine, but a skeleton or ghost would probably be out of luck. Heck, a golem can even drink a potion if they're built properly.
Also note, Complete Arcane gives examples of potions in alternate forms such as spell tiles, bone talismans and such. Basically the form the "potion" takes just needs to meet certain criteria, but is otherwise up to the creator. The three pertinant requirements here would be that the item is expended by its use, the item must be manipulated in some way in order to facilitate its use, and that such manipulation provokes an attack of opportunity.