AFAIK kmz exports only from the 3D window, so a dwg wouldn't be visible in the resultant file unless it contained 3D info. So you would probably have to open or save your dwg as a library part to see it in GE.
So, without testing it, I would think the workflow would be to
place the dwg as a library part into the project, import the kmz file, then export them both out together?
Cheers,
Link.