It is executing the same command for both file formats:
<delegate decode="cgm" command="cmd.exe /c ("uniconvertor" "%i" "%o.svg") & (move "%o.svg" "%o" >nul)"/>
<delegate decode="dxf" command="cmd.exe /c ("uniconvertor" "%i" "%o.svg") & (move "%o.svg" "%o" >nul)"/>
It seems to use SVG as an intermediate format. Have you tried running uniconvertor on the command line and examined the resulting SVG?