The Open and Import features have been since GIMP 2.8x I think … don’t remember much. So the stable repository should at least support this or newer GIMP version.
But I don’t know the drag and drop feature, or the darktable integration with GIMP. So can’t say much on this.
My workflow is to use darktable and GIMP separately. Use darktable to do some basic RAW image processing and save it into jpg or png format, then import those files with GIMP to do advanced image processing. I never try Import RAW image directly from GIMP though.