IslarattaI You were absolutely correct. Not only does it work like this, but it can be applied to any base, plutonium-DLC, or custom maps with no issue.
Shame it doesn't work for GIGN v Spetsnaz, PMC vs Militia (Favela or the custom MW2 Carnival port on this site could really use these). Would need some type of access to both factions .arena files, which aren't present.