It's all good, guy. At least you didn't show up to a game with a build based around that single concept only for the DM to point out that the feat didn't work that way.
As mentioned above, if an object would have to make a save then an undead has to also.
It's rare for it to happen, but when it does the undead can be at a significant disadvantage since they don't get a bonus from their Constitution score.