Correct, so long as you're talking about POIs. The game and RWG can both traverse directories in the Prefabs folder to find POIs and there are no XML entries for POIs.
But when it comes to Parts (built like POIs), they must be in a Prefabs/Parts folder in the modlet. The XML entries for Parts are in each POI's XML file.
When it comes to Tiles (built like POIs), they go in a Prefabs/RWGTiles folder AND they have entries in the rwgmixer.xml file, which you add using XSLT in your modlet.
When it comes to Decorations that are built like POIs, they can go in any folder under Prefabs and they must have entries in biomes.xml file, again via XSLT.