I also had to repair the script there anyway, so I may have overlooked something. Let's see:
No, it's just that certain characters aren't even loaded on that map, so it's impossible for them to show up. Cid HAS to be allowed, because you can play as him during the Huge Materia quest. If his model wasn't loaded on the map, then you'd end up with invisible character there.
Vincent and Cait will never show on that map (not unless someone were to edit them in - but there's no point). Red XIII, Yuffie, Tifa, Cloud, Aerith, and Barrett all have their own dialogue for the bridge scene. Cid is only loaded because he has to be later in the game. It's nice to see the programmers/writers bothered to give Yuffie some fun dialogue there.