A grep for GetVtkImageData() gives the following occurens in MITK:

mitkExtractSliceFilter.cpp
mitkImageSource.h
mitkImageSource.cpp
mitkImageToSurfaceFilter.cpp
mitkSurfaceToImageFilter.cpp
mitkImage.h
mitkImage.cpp
mitkImageVtkReadAccessor.h
mitkImageVtkReadAccessor.cpp
mitkImageVtkWriteAccessor.cpp
mitkImageVtkWriteAccessor.h
mitkImageVtkLegacyIO.cpp
mitkImageVtkXmlIO.cpp
mitkSurfaceVtkMapper3D.cpp
mitkVolumeDataVtkMapper3D.cpp
mitkExtractSliceFilterTest.cpp
mitkImageTest.cpp
vtkMitkThickSlicesFilterTest.cpp
Tutorial\ITKAndVTK\mitkWithITKAndVTK.cpp
Tutorial\Step7\Step7.cpp
mitkLabeledImageToSurfaceFilter.cpp
mitkContourModelUtils.cpp
TensorImages\mitkTensorImage.cpp
TensorImages\mitkTensorImage.h
QBallImages\mitkQBallImage.cpp
QBallImages\mitkQBallImage.h
mitkVectorImageVtkGlyphMapper3D.cpp
mitkExtractDirectedPlaneImageFilter.cpp
mitkExtractDirectedPlaneImageFilterTest.cpp
mitkImageWriter.cpp
mitkGPUVolumeMapper3D.cpp
mitkVectorImageMapper2D.cpp
mitkLabelSetImageToSurfaceFilter.cpp
mitkContourModelSetToImageFilter.cpp
mitkManualSegmentationToSurfaceFilter.cpp
Interactions\mitkSegTool2D.cpp
mitkOverwriteSliceFilterObliquePlaneTest.cpp
QmitkSlicesInterpolator.cpp

The following files contain only definitions / provide data. Therefore no check is required:

mitkImageSource.h
mitkImageSource.cpp
mitkImage.h
mitkImage.cpp
mitkImageVtkReadAccessor.h
mitkImageVtkReadAccessor.cpp
mitkImageVtkWriteAccessor.cpp
mitkImageVtkWriteAccessor.h
TensorImages\mitkTensorImage.h
QBallImages\mitkQBallImage.h

Within these files GetVtkImageData is returned for methods with a different name. E.g the use of these methods has also to be checked

TensorImages\mitkTensorImage.cpp -> GetNonRgbVtkImageData
QBallImages\mitkQBallImage.cpp -> GetNonRgbVtkImageData