From the macro posted earlier:
  Py##child##ArrType_Type.tp_base = &Py##parent2##ArrType_Type;

tp_base is *not* PyInt_Type, so I was wrong when I said that the dominant base was int.
This is wrong IMO: tp_base should be int, for the type to be correctly initialized.

Compare:
>>> from numpy import *
>>> print int_.__bases__, int_.__base__
(<type 'numpy.signedinteger'>, <type 'int'>) <type 'numpy.signedinteger'>
>>> class C(signedinteger, int):
...     pass
... 
>>> print C.__bases__, C.__base__
(<type 'numpy.signedinteger'>, <type 'int'>) <type 'int'>