Oh wow, this is interesting, to me at least.
As I mentioned before, the PS2/Wii versions of the game were pretty much built upon NFS Carbon, so I am not too surprised by some of those cars from Carbon being hidden in this game. However, I didn't even know the 370Z was in this version of the game. According to NFS Wikia, it's a multiplayer only car and since I never played multiplayer in Undercover, I was completely unaware of the car's existence in this version of the game.
Man I
really hope we get a save like this for the PS2 version. Being able to drive the firetruck from Carbon again would be great and same could be said the motorhome. Felipe said in the comments he had a modded save for the NTSC version and I am hoping he will post it. I would ask him myself, but I don't want to create and entire channel just for that.
The interesting thing about the AI cars is, just like Carbon, they don't crash the game when they get wrecked and they even have their own engine sounds.