As you can see from the screenshot, Gorm is now able to load nibs just fine.
Gorm should be able to save nibs in the next few weeks. This is a huge step forward for GNUstep. Builder and Loader classes have been added along with a factory class which gets the appropriate builder/loader for a given format. Gorm has also been changed so that it is effectively format agnostic. This means that it can accept any format that a builder/loader class can give it.
In addition to the above Gorm also uses the NSDocument* classes instead of implementing it's own framework.