The init method that comes up for int, str, float, etc is just the object init:

assert int.__init__ is object.__init__

Probably the thing to do is grab any init methods that aren't the object.__init__ while stripping out the dataclass-created init methods? Maybe something like:

import warnings

if cls.__dataclass_params__.init:
    for pcls in cls.mro():
        if pcls.__init__ is not object.__init__:
            try:
                d_params = getattr(pcls, "__dataclass_params__")
            except AttributeError:
                warnings.warn('Found a not called init')
            else:
                if not d_params.init:
                    warnings.warn('Found a custom dataclass init')