Belegorm: Vice and Mature were considered "missing", but they've held true to their "We'll meet again under the full moon..." stance. Even Terry is suprised in his XII win quote to Mature: "NO WAY! You actually survived that?!?" There's a play at them being ghost in XIII's color palettes for each (they're transparent), but at this point, they seem to be extra-special servants of Orochi, whom seem to be the first on-call line of defense / investigation for him, when things go haywire. They also seem to have an odd bond with Iori, neither really being THAT mad about what he did to them.
As for new characters in XII and XIII, not exactly. Hwa and Raiden were new to KoF, but most of what's been considered "New" in these past 2 games, has been the re-freshing of the characters in the game. Characters like Chin, Kensou, Iori, and Ash have almost been re-created for XIII. SNKP is in a spot where they want to bring old favorites back, moreso than introduce new characters, as they already can't even properly serve all the characters that even XI introduced, such as Malin, Momoko, and Oswald.