Those are link errors, so in the Visual Studio project, please check that the GDCM libraries (especially gdcmMSFF) are being linked. You can also open your CMakeCache.txt in a text editor and search for gdcmMSFF, it should be listed as one of the dependencies of vtkDICOM.
The latest version of vtk-dicom is source compatible with VTK 7.x, VTK 8.x, and VTK 9.x.
For the QVTKWidget, see the topic yet-another-qvtkopenglwidget-renaming.