Hey Niner!
The proper method of nickel-chrome plating over imperfections will usually not hide noticeable scratches. The bumper can (usually) be polished by the plating shop after you finish your patching. The chrome will be stripped by the plater, since it's usually only 10 - 20 microinches thick. Its function is to prevent the nickel from tarnishing.
The existing nickel is probably 0.0002" to 0.0006" thick. Check w/ your plater to see what the maximum scratch depth he can polish out.

From Homer the Chromer.