Hi Kristof, glad you got it working!
It's a simple engine, and entities can only use AABBs for collision. Their bounds are defined in a RosaCollision component; look for the variables HalfExtentsX/Y/Z in the config files.
Static geo can use more complex collision, by exporting one or more convex meshes along with a renderable mesh (in the other export script, xmlbrushexport.py). In this game, I think I only used the simple box and wedge primitives in Raw/Brushes/Core.
The ExpectedVD assert is probably because the mesh doesn't have a UV vertex stream, as you guessed. Doing an auto unwrap in Blender should fix it.
David