My understanding of things is that if you're missing a g3d file, the game will show a cube instead, right? For me, the game crashes, unable to load the tech tree instead of using placeholders. However, placeholder textures do work. This is true for 0.3 and 0.3.1 both. This is using the addons folder, as I haven't tested it by messing with the main directory.
Linux Mint 32bit.
Glest Advanced Engine: Error log file.
XML Error in techs/magitech/resources/gold/gold.xml:
Exception caught loading 3d file: techs/magitech/resources/gold/gold.g3d
PHYSFS_openRead failed: techs/magitech/resources/gold/gold.g3d
Error: No such file or directory
<tons-more-similar-errors />
While this is very useful for me, as I use the error log as a "to-do" list, I'm pretty sure it's not the intended behavior.