I've been cured of vampirism numerous times for the Face Changer and every time I've re infected myself I've had Khajiit fangs. If anyone here has an account on the wiki they should probably go and take that part out, it's just added BS.
I think I've also gotten to as close of a confirmation that the beast race vampires do not lose their fangs in Dawnguard. I did this by creating a test mod that adds the fangs to all Khajiit, and then started a new character. The new character had the fangs as expected. Then after a save for the character was created, I exited the game and disabled the mod, and then reloaded. Boom, no fangs, and then reloading the save after re-enabling the mod brought them back. When activated, this mod also gave one of my real Khajiit characters fangs as well. Though for some reason it wasn't giving NPCs fangs.
So therefore, there is no way that Dawnguard removes the special fangs for the beast races at all, since the fangs do not bake into save files from what I've been able to tell.