You know what -- there needs to be a FF summon in BBS, I'm not even joking.
ChocoboEither one of those or they can always make KH deviations of popular FF summons.
Mog/Moogle
Tonberry
Cactuar
Moomba
A KH-ified BahamutAnd so on. I mean, every magic spell (as well as all the FF characters) in KH are deviations of FF spells (and characters). They could do the same with summons -- it's not as big of a deal as some people make it out to be. >.>
A KH-ified Shiva
A KH-ified Ifrit
They Should use the FF Summons from Final Fantasy Fables: Chocobo Tales. In that game, they are cute and not evil.