The hood is a pretty thick hunk of metal...don't worry about possible rust effects (if any), as it will be surface rust at best.
A body shop should be able to repair the damage fairly easily. It won't be perfect however, unless a whole-hood respray is in order..
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car