I watched an episode of Uncle Grandpa to see what all the fuss is about. How on earth will that episode be any good? That show is just random shit.
Uncle Grandpa is a cartoon in the purest sense. It takes all the liberties and the only liberties that one can do in animation. Just because it's weird and silly doesn't make it bad. It's just a different style that SU. UG has its serious moments, just as SU has its silly ones. I have a feeling the crossover will have to meet in the middle. I am putting my trust in the creators of both shows, clearly they wouldn't have gone through with it if it was something that they felt wouldn't work.