Metals don't feel pain, so i doubt they will get hurt.
It is easily scratched, but I put a Best Skins Ever on it right when I got my iPod and it's still as shiny as then. Don't know about denting, seeing as I've never dropped it (the BSE adds a firm grip to the back too).
And I don't know about hollowing...unless you drop your iPod in acid? 😕