I've tried exporting from Maya & Lightwave, and I can import between the two no problem, all the geometry appears exported to the DAE files.
However, when loading any of the editors, importing a DAE/COLLADA file, converting it then loading the GCF via the dialog, I always get no geometry. Its just a blank bounding box. I've ensured that UVs exist for every surface, painted them all with a single texture, etc., and I still can get any geometry imported.