Clipping paths in Tiffs are not a standard tiff feature. Much like transparency within tiffs, clipping paths in tiffs are an Adobe feature. I can't state whether or not Gimp can do anything with the path if it exists.
Customarily if a Photoshop .tiff has a clipping path, you would Place the image into a layout applications such as InDesign or QuarkXPress and then set the image to use the embedded clipping path to designate where transparency should be indicated in the (rectangular) image.
The use of clipping paths in tiffs is very similar to how one would use transparency within a .tiff file for use in layout applications - for text wraps and other object interactivity.
Within the raster editing application itself, the path is generally of no great use. Again no knowledge of GIMP here, but with Photoshop you could select the path, convert it to a selection then create a Layer Mask based upon the path. Essentially converting the clipping path to transparency.