Hi. If you mean:
Vectors imported from Inkscape into GIMP lose quality, but vectors from Inkscape to Scribus do not, there are some possible solutions:
GIMP does not currently handle vector shapes as vectors, so when you import, GIMP will ask at what resolution you want your vectors to be rasterised (converted to pixels). This dialog pops up when you choose File > Open, or File > Open as Layers, and is called "Render Scalable Vector Graphics".
In this dialog, you can get higher quality result by:
1. Increasing the width and height (in pixels) of the imported graphic
2. Increasing the Resolution (usually a value of 300 or higher for printing resolution). This will automatically adjust your height and width in pixels to higher values.
Scribus handles vector graphics as vectors, so vectors imported to Scribus will still be vector-crisp.
Hope this helps. :)
-C