I am pretty confident that it's absolutely impossible to display a
DWG file in OL3 currently. Theoretically it could be possible to
write a custom ol.format that parses any file type, but there is
none right now.
I don't even believe that there is a way to display (directly) a DXF
file either, even though it's a text format with documentation from
So what to do? I would try GDAL's ogr2ogr to convert the DXF to
GeoJSON, which is supported by OL3. However don't expect the result
to look exactly like what you see in AutoCAD.