The contributors cited in ContributedFurnitureCatalog.properties didn't express their wish to release their models under the GNU GPL and I fear that some of them are unreachable to ask their opinion about it.
If you want to use only GNU GPL 3D models, just edit with a zip tool the [font=courier new]Funiture.jar[/font] file found in installation folder of Sweet Home 3D to remove all the files that start by [font=courier new]ContributedFurnitureCatalog[/font].