Found an alternative source for Inkscape.
Inkscape doesn’t seem to offer a DWG or DXF Export format.
So I look in Save As instead of Export.
It doesn’t list DWG as an option (though DXF is explicitly listed), but says it will guess from the file extension.
So I tell it to save as ARCH-01.dwg, import it into SU, and BINGO, it works.
AND it makes a reasonable effort to import the (raster) text, which the online importer didn’t attempt.