Using qgis2web I created a Leaflet map that has a vector layer, a raster layer and OSM background. I included in the map the layer list ("Add layer list" option in qgis2web). The vector layer appears in the layer list and I can turn it on/off. However the raster layer does not appear in the list. Is that the intended behavior? Using OL3 I can turn rasters on/off.
OK, this was a bug. I've committed a fix to the master branch on Github. If you download just the file leafletScriptStrings.py, and overwrite your copy, the bug should be gone. Do let us know.