Hi JZ,
Sorry for the late reply...
So just what I thought - the kml filedefines the geometry itself.
SketchUp can only read *.dae files that are "archived" inside the kmz file. SU generally puts them into a subfolder called "models".
Rename your kmz extension to zip and when opening it, you can see that there's just a single kml file.
Is there any other way your program can export to kmz (or dae)?