Flo Rida planned on chillin' at the Pool After Dark at Harrah's Atlantic City Friday night following a concert at Stockton College, but he ended up doing another show. R&B artist Iyaz was scheduled to perform at Harrah's, but his flight from the Bahamas was canceled.When Flo Rida arrived and heard what happened, the rapper hopped on stage and played four songs, then dove into the pool as DJ Louie DeVito kept the music going. Flo Rida sipped Moet Rose champagne and Grey Goose in his VIP cabana. And elsewhere in AC . . .Tennis great Venus Williams hosted the Caesars Tennis Classic after-party at Dusk inside Caesars, where Andy Roddick took the microphone and led the crowd in singing "Happy Birthday" to a fan. Roddick and Williams danced to DJ Sat-One's tunes..."American Idol" judge Kara DioGuardi, husband Mike McCuddy and friends partied at mur.mur inside the Borgata after her performance Saturday night at the hotel's Music Box theater. DioGuardi joined DJ Sky Nellor in the booth, where Nellor spun dance hits of songs DioGuardi helped write by artists Jason Derülo, Iyaz, Jim Jones, and Cobra Starship.