I am using a One Up rack on my 2004 with the integrated hitch receiver. I have a "base" model One Up with a 1.25" receiver and a 2" adapter. It works with the integrated hitch with no modifications. Mine has no pin, it's held in place exclusively with the expanding ball. As an aside, I do not recommend this setup because it works itself loose on washboard pretty quickly.
I have read that the shape of the integrated receiver necessitates light grinding for some adapters/racks to fit; I think I've read that 2" One Up racks need a little trimming in order to slide easily into the hitch.
Edit - I'll also note the tailgate hits the rack so you can't put any weight on the tailgate with the rack installed. A swing-out rack adapter would remedy that problem.