Pretty much you've got it. You just stick the the dsp_firm_dumper folder into a 3dsx folder on the root of your SD card and run it from within the Homebrew Loader (be connected to the Internet the first time you use HBL, the CIA version of the HBL should download an appropriate payload for your system menu version if there isn't one).
ScummVM games can be in any folder you want really (make sure you copy the files in that archive with the CIA to your the root of your SD card btw, ScummVM needs those). Lots of different game versions should work...talkie CD versions, floppy versions...IIRC both the mac and Windows versions should work. You're probably covered regardless of what version you have unless it were missing files or something.