If you try to make a project with GM Studio which contains tiles, and then you open this project with LateralGM, it will import the tiles, but not correctly : all the tiles instance have the same Id (0), and it's not possible to move them or to delete them with the right button. It's only possible to delete them with the delete button. Still it's possible to add new tiles.
I made a small test project, with the logo of ENIGMA as the tileset.
Here is a zipped version of the gmx project made with GM Studio :
https://dl.dropboxusercontent.com/u/29802501/test_tiles.gmx.zipAnd here is the converted project :
https://dl.dropboxusercontent.com/u/29802501/test_tiles.egm