This is the best evidence I could find right now. It doesn't say that R* is going to be there for sure, but it does say that Take Two is going to be there. Since R* wasn't at E3 and Take Two was at E3 and is supposed to be going to Gamescom, I'd imagine they wouldn't show the exact same thing that they did at E3. At least I hope so anyway...
http://rockstarinformer.com/179/take-two-interactive-to-attend-gamescom-2012/