You must visualize RasterTileSetModel instances with view/tileset/RasterTileSetLayer. You typically configure raster layers with the BASE LayerType, because they often show background data:

Program: Creating a RasterTileSetLayer with the BASE layer type 
const rasterLayer = new RasterTileSetLayer(model, {
  layerType: LayerType.BASE,
  label: "Earth imagery (Fusion)"
});

map.layerTree.addChild(rasterLayer, "bottom");

Raster services, such as Web Map Services (WMS), also support transparent raster data. If you use transparent raster data, you can display two or more raster layers on top of each other. You can display raster data with roads or waterways on top of a raster with satellite imagery, for example. You must configure such overlay raster layers with the STATIC or DYNAMIC LayerType. Those are the layer types that you can place on top of BASE layers.

When LuciadRIA visualizes raster data on a WebGLMap, it must have access to the data. See CORS problems when visualizing raster data on a WebGLMap for more information.