Thanks for posting the feat! These discussions are difficult w/o them.
I think it's pretty clear from the wording of the feat that it does not allow you to sneak attack creatures normally immune. It says that it any attack you make is a sneak attack. Big deal. If you flank a golem, and make an attack, that's still considered a sneak attack. However, because he's a golem, he's immune to the extra damage. Same applies here. From the SRD:
Note the bolded line. A creature who is immune to critical hits is not vulnerable to a sneak attack. You can attempt to make one, just as you can attempt to critical it, but that doesn't mean they'll take extra damage if you succeed.
I suppose there's a better case to be made for allowing the feat to let a rogue make sneak attacks against foes with concealment, since the feat says that any AoO is a sneak attack, but I still think that's an overly liberal application of the rules. All this feat does is add an additional condition for a sneak attacks. It doesn't change any of the other rules regarding it.