It's a rumor, well kinda.
Steven R. McQueen is set to make some appearances on Arrow as Dick Grayson/Nightwing. Colton Haynes is rumored to come back as Roy Harper/Red Arrow. While Megalyn Echikunwoke might become Mari McCabe/Vixen in the show. Willa Holland is set to play a part in the show too as Thea Queen/Speedy. While Raven and Starfire are set to be cast later and Echo Kellum will be Mr. Terrific in the show.
It's just a rumor, but they might become a spin off. While Matt Ryan will move to Legends of Tomorrow as Constantine.