Hi guys,
I am working with unstructured grids at the moment and there was a change in vtk 6.1.0 which allows unstructured grids with arbitrary memory layouts to be integrated into VTK (i.e. given your representation, there's no need to create a fully fledged vtkUnstructuredGrid, but rather create an adaptor class to implement the vtkUnstructuredGridBase interface - see http://www.vtk.org/Wiki/VTK/InSituDataStructures). This is really convenient and changing all the references in MITK from vtkUnstructuredGrid to vtkUnstructuredGridBase this also works for MITK.
The patch is attached. I think it makes sense to integrate it with MITK and it would take very little time to do so.
All best,
Rostislav.