The blend of country and hip hop is actually a lot more obvious and reasonable than many would expect. Both genres represent a culture of inveterate story telling and exceptional rhythms and choruses. They are also both distinctly American genres, telling truly vivid American stories. Themes of pride and love are integral, and it was only a matter of time before a couple of renegades in their genres would cross the lines. The first examples I heard were Brad Paisley and Nelly getting together for Over and Over, and Kid Rock joining Sheryl Crow for Picture.
With Nelly now joining the Florida Georgia Line, he is establishing a niche for collaboration, and opening up whole new audiences. I am impressed with his openness to such innovation. Of course, growing up in the Midwest, Nelly was always going to have bit of a country drawl to his songs. And his use of Smokey and the Bandit motifs in his video for "Ride Wit Me" indicated a bit of country even in his earliest writing. And I would say that his collaboration with Kelly Rowland on Dilemma, while truly an R&B song, actually had a real "country" feel to the tone and story.
Of course, we shouldn't forget other collaborations that fuse the genre for one singer. In that I'm thinking of Jason Aldean's Dirt Road Anthem. Aldean's collaboration with Ludacris on this song actually angered many country music purists, but in true renegade fashion, both artists persisted and produced a quality song.
Finally, no discussion of this cross-cultural collaboration would be complete without mentioning the most controversial example - The Accidental Racist featuring Brad Paisley and LL Cool J.