I'm running the 22t dp on my turbo GC with the 22t ... WRX dp should fit fine mated up to any wrx/sti exhaust. The 22t dp is actually about 2 inches shorter, so I actually cut and welded in a piece of pipe so it would be long enough. If the catback is a non-turbo catback, you'll need to get the flange rotated about 90 degrees, but otherwise should be fine.
But yes, if you take a wrx/sti exhaust, it will bolt right up, except for maybe one of the hangers