Succubus race works perfectly with Dawnguard. No required file is needed. Just one file even if you don't have Dawnguard. To become a vampire you have to be infected by an other vampire or complete the main quest of Dawnguard and chose the vampire faction. When you are a vampire, you loose the succubus drain, you can use the regular vampire drain spell instead.
It's compatible with Better Vampires by Brehanin mod. It enhances game-play when playing your succubus character as a vampire.
Thanks to Himika and his/her great RaceCompatibility Racial Compatibility - compatibility with other mods improved . Succubi can now become vampires without any compatibility issue and overwritten files.If you change your race during your game, once you get your vampire powers (by being infected) open the console and write "player.setrace SuccubusRaceVampire and you will become a "full" vampire.