Believe it or not, Flo Rida does, in fact, rap. You won't hear him on hip-hop stations, and his name never comes up in discussions about great rappers, despite his intense success. This is because he makes club music that seems to share no real estate with the rest of rap music, unless you attend certain Top 40 clubs.
Top 40 and popular rap used to occupy the same space, particularly in the late '90s and early 2000s, but today's rap mainstream has pulled further from pop music's mainstream. The few remaining "hip-hop" artists in that world are the descendants of the Black Eyed Peas, the first group to make radical gestures towards dance music's four-on-the-floor beat.
Flo Rida isn't a distinctive MC, and doesn't seem to have much in the way of hip-hop fans, so hating him is a bit fish-in-a-barrel. But even his big club hits, like 2011's "Good Feeling," are knockoffs of more successful club tracks (Avicii's "Levels.") He's an easy target, although he's less rapper than he is pop star, so much of the hate from hip-hop heads feels unnecessary.
It's 2012 and the monoculture is dead; you have to go out of your way to hear a Flo Rida track. Instead, he's a reminder to rap fans that hip-hop's relevance to the mainstream is ebbing.