As far as I know it just adds extra armour to a vehicle and does make it indestructible.
This was tested with the option on, then you get into a driving vehicle such as a truck. You can drive around fast, smashing into things, and never have the vehicle break down or explode. I did not test against rocket launchers coming at you from the enemy or whatnot. It likely will not prevent you from blowing up when you nose dive a plane into the ground, etc.
I have no idea why the cheat won't work for you but, as a workaround, you can try using the trainer's options for infinite supplies or infinite ammo and other stuff forgot which one is exactly but while active, you can sell all your loot over and over again. Like, you hunt a bit, collect skin enough for, say, 5k, then activate the cheat, go to shop, sell all loot (sell one item first to make sure it's working) rince and repeat you can get to max money that way it'll take a few minutes tho
Brilliant workaround! Thanks alot!