I don't remember a decision being made that all zombie roleplayers will be playing as civilians for the last mission. I believe some will be allowed to play as paramilitary or even military, if they have the proper credentials, but don't take this as the final word.
I saw this in the description:
"Volunteers will revive free admission to event and be able to play as survives on the last missions."
I may be wrong, but what this looks like is that "Civilian Survivors" is what its referring to, because Paramilitary is called "Paramilitary Forces".