I started this thread, but realised I had found a solution before posting. I posted anyway for others reference and comments.
sudo apt-get install unoconv
Then , to insert an odg into Lyx, insert as Graphic in Lyx.
In Preferences -> File Handling -> File Formats
Enter a new vector graphics format: OpenOffice Draw / odg
Default display as PDFLATEX.
In File Handling -> Converters
Add new OpenOffice Draw -> PDF (create a separate entry for every PDF option - not just PDFLATEX)
Converter: unoconv -f pdf $$i
It should then work.