As far as the floor and seat mounts being the same, the longer SUVs (Burban, Yukon XL, Escalade ESV) all have the same third row seat mounts made into the floor. The Tahoes and Yukons have a slightly different setup, like someone mentioned they have mounts bolted to the floor and have a split bench instead of a solid third row seat like the Burban and Yukon XL has.
Personally, I would try and see if you could get a split third row seat from a Tahoe and get the mounts and see if you can fabricate something to get it mounted. The good thing about having the split seat is the fact that you can put just one side of the seat in if you want to. That would come in handy if you need just one more seat, but also still need a bit of cargo room to put groceries or something.