This makes sense... though how about swapping out Memphis and Minnesota? Because a division with DC, Philly, Ohio, and Memphis is just weird.
East:
Raptors, Celtics, NY Knicks, NY Nets ("Atlantic Division" or "Northeast Division")
Wizards, Pistons, Cavaliers, and Sixers ("Great America Division") - couldn't think of a better name, but it works IMO... think about it
Bulls, Pacers, Bucks, and Timberwolves ("North Division", "Great Lakes Division", "Rust Belt Division" or simply "Lakes Division") - probably stick with "North"
Hornets, Hawks, Heat, and Magic ("South Division" or "Southeast Division")
West:
Spurs, Mavericks, Rockets, and Pelicans ("Sun Belt Division") - can you think of a better name than that?
Thunder, Nuggets, Jazz, and Grizzlies ("Frontier Division" or "Heartland Division" or "Central Division") - it works
Lakers, Clippers, Suns, and Vegas ("Desert Division", "Cactus Division", or "Southwest Division") - any other ideas?
Kings, Warriors, Blazers, Sonics ("Cascade Division" or "Northwest Division") - personally I like the Cascade idea