Different B-Schools have different sets of priorities while designing their admission process. This stays same even between different IIMs, both old and new. The priorities assigned to academic performance, CAT scores, work experience, the scores in the GD/PI and interview sessions vary quite widely between these institutions, and even yearly. So, we can say that there is no accepted fact that lack of a formal work experience will prevent anyone from getting into IIMs.
Significant push has been made to make the campus and environment of B-Schools more inclusive and diverse, that also includes giving fresh graduates a decent chance to be a part of them, and IIMs are no exception.
All things said and done; one must do what they can to compensate for any lack of work experience. Having decent academic record throughout, extracurricular activities that add to profile, good communication skills and knowledge about current affairs, and most of all, a decent CAT score that can get you into admission process of any B-School.