CTK just adds many features to VTK (DICOM browser, GUI widgets for medical image visualization, helper classes for Qt-VTK integration, etc) does not replace VTK. So, if rendering works in 3D Slicer then you can surely make things work by using CTK only or even just using VTK. You just need to figure out what pieces you need to port from there. Or, you can take ideas from how Paraview creates its rendering widgets.