SPH interpolators should have an option to set the name of the CutoffArray
vtkSPHInterpolator provides a way to set an optional cutoff distance for each point in the input. A scalar array name can be set via the macro SetCutoffArrayName()
example: interpolator = vtk.vtkSPHInterpolator() interpolator.SetCutoffArrayName("SmoothingLength")
the issue is in the XML code in ParaViewCore/VTKExtensions/Points/points.xml where only two StringVectorProperty are defined to set the Density and Mass arrays.