Just did some comparisons using my DJ software. First off, the Goog tells me that the original Dreams is in C major (no surprise there.)
Dreams (Deepend Rework) (key of F) is definitely pitch shifted, hugely. Mostly for artistic effect. Stevie is all but unrecognizable.
Dreams (Kaskade & L'Tric Remix) is a tougher one to pin down. I downloaded KeyFinder and it also thinks the remix is in D minor. I think the remix might change keys in the middle. I mixed it with song sin the keys of Am, C and Dm, and none of the mixes really clued me in definitively. Of course I am the farthest thing from a trained musician.