The feds mandate a minimum cetane level for diesel fuel that is sold in the US of A and all diesel engine manufacturers that sell vehicles here know what it is and build their engines to run on it. So you do not need to worry about running into fuel you can't use.
Just about every diesel additive you will find will state that it improves the cetane level. The question is 'How much ?'. I'm guessing it's barely measurable. I also run the Ford additive (PM22A), but I do that to improve the lubricity of the fuel.
Do not confuse cetane improvement with lubricity improvement or with fuel gelling up in cold weather. Those are 3 entirely separate issues with 3 different solutions. And Bio-diesel is a whole different kettle of fish.