Solved.
For the record:
Code:
# Additional imports
from ctypes import pythonapi, c_void_pointer, py_object
# Setup arguments and return types
pythonapi.PyCObject_AsVoidPtr.restype = c_void_p
pythonapi.PyCObject_AsVoidPtr.argtypes = [ py_object ]
# Convert PyCObject to a void pointer
hWnd = pythonapi.PyCObject_AsVoidPtr( view.winId() )
# Then use hWnd
viz.go( viz.EMBEDDED, window=int( hWnd ) )