Since both meat hooks and Undead happen at the same time (when the unit is defeated), you can choose which order to resolve them in. Which effectively means that you can choose to put the Undead Baddie on Meat Hooks and have it not come out a second time.
It's very powerful for Carcass to be able to prevent an Undead Baddie from coming back, but Undead is a pretty rare skill. Also note that it would have to be Carcass dealing the defeating blow for him to be able to use Meat Hooks - if another Gearloc defeats the unit, Meat Hooks won't trigger.