If you're looking for a specific music genre that you can put a label on and call it Steampunk Music, I've got bad news for you: There's no such thing.
Steampunk music is whatever Steampunks listen to. It can be anything from Opera to Country, from Jazz to Punk. It's the theme that makes it Steamy.
A song about a pirate is not necessarily Steampunk. A song about an airship pirate is.