I use gimp/inkscape as a workflow, often using inkscape to create elements or to do text on path labeling easier.
So I made this set of scripts for gimp (that all end up under the Layer menus) to implement file linked layers:
http://ffaat.pointclark.net/incoming/scripts/file_linked_layers.scm
You can... Load a new File Linked Layer (loads up an image as a layer and sets the layer name to "@FL@<full file path>".) Reload All File Linked Layers (looks though all the layers for ones where the name starts with the "@FL@" flag and reloads them.) Reload File Linked Layer (reloads the active layer if it has the @FL@ flag.)
So when I update things in inkscape and export a png (full page) then to the "reload" script, the layer gets replaced.
Right now it doesn't transfer layer masks, blend modes, or opacity to the newly loaded layers, but that could be added if necessary.
Not super integrated, but easier than manually reloading layers. (It was developed in answer to this request: http://lists.xcf.berkeley.edu/lists/gimp-developer/2009-June/022567.html )
-Rob A>