If the movies can have a Flash in spite of the TV show, and Doom Patrol can have a Cyborg when there was already one in the Justice League movie, there's no reason why they can't have the same character played by different actors in Titans and the Arrowverse shows. I can imagine it happening with Batman (both Titans and Batwoman have reason to use him) or Superman (Titans has Superboy and Supergirl introduced a Superman who's getting his own show).