RAW - looks legal
Are you asking as a GM or as a player of an undead character? As a player I wouldn't do it, feels cheesy and you might get the stink-eye from your GM. As a GM I'd only even consider adding the feat to an undead if I wanted the encounter to be more special and difficult.
I see no problem with it.
It doesn't seem cheesy to me either. Is it cheesy if I take it with my immune to fatigue Barbarian/Oracle?
It locks down your immediate action every round for a moderate benefit. And to "exploit" the immunity to fatigue you have to actually get immunity to fatigue, which is nontrivial to do permanently. That's fine.
I see no problem with it.
It doesn't seem cheesy to me either. Is it cheesy if I take it with my immune to fatigue Barbarian/Oracle?
It locks down your immediate action every round for a moderate benefit. And to "exploit" the immunity to fatigue you have to actually get immunity to fatigue, which is nontrivial to do permanently. That's fine.
What feels cheesy to one is fine to another. I gave the answer and then gave my opinion. To me an Oracle/Barb getting this feat is only a tiny bit cheesy for the simple reason of the level that it becomes useful is around level 10 and you give up BAB as well as progression of your rage powers.
This is very much different than starting off at level 1 as a player undead, and oh did I mention the undead I am has DR as part of it's template! That is where I felt this was going but I could be wrong.
It's the playing an undead that's the cheese.