"Activating" the dummy actors?

It's because the character is simply not recruited or set up/loaded rather (event code). Testing with the first battle event dialog (Whelk) if you try loading Vicks' name as say,
Sabin < A$05 >, it shows as blank. But if you load Vicks as < A$21 >, which is VICKS, it shows up correctly, because his name's been loaded at the start of the game:
CA/5E5A: 7F Change character $0F's name to $21 (VICKS )

Along with his other properties. It might just be the name loading that does it for the battle dialog, but I'm not positive. I'm not too sure offhand if you could possibly load up all the unused characters in order to have them all activated for battle dialog, without effecting the playable characters and whatnot.