Yeah, you need a synth. That's where the sound comes from. The map just directs the notes.
If you already have the MIDI track set up with your synth as the output, selecting a drum map will just be a somewhat transparent in-between step. In the map itself, you can tell it where to send the notes, but you must have an active synth.
If you use TTS-1, a map is ready made, just waiting for you.
In your MIDI track, set the bank to 15360-Preset Rhythm, and the patch to any named drum set.
Now the Piano Roll will show the GM drums, instead of piano keys.
There is also a preset map for Session Drummer.
With EZDrummer, I use a limited GM map.
And you're right. Once you get it, you're good to go.
edit: Man, I type too slow.