GR00T: Basically, all the installers are classic installers and Galaxy just fetches those if you use it to install your games.
Actually Galaxy doesn't fetch the installer, because it is the installer. :P It fetches the (compressed) game directly, and when it updates - it updates the game files directly (with a diff patch when possible).
You can then still launch the game directly with Galaxy turned off, or remove Galaxy - if you wish - and still play the game with no issues and no Galaxy features. There should be no real difference when installing through "backup installer" (maybe shortcuts or installation folder suggestion). You just have the backup installer then. :)
Just to be clear: you can download backup installers through Galaxy too.