A cursory Google search (2009) didn’t turn up anything promising in regards to comparing Rudolf Steiner and Sri Aurobindo. Hopefully this will help:
This longer essay summarizes the basic elements of the spiritual-cosmological worldviews of two of the most important modern, integrative spiritual thinkers: Rudolf Steiner and Sri Aurobindo. Upon this foundation a brief comparison is made between the two systems and the two men.
Thanks to John Elwyn Kimber for pointing me to this webpage where Pavitra, a disciple of Sri Aurobindo, records her meetings with him (see pages 4 and 5 specifically). Pavitra and Aurobindo both say that they know some theosophists, and know of Steiner, and by Aurobindo’s responses I get the sense that he at least knew something about Steiner specifically. However, it seems that he is being treated primarily in the same vein as theosophy (which would make sense from the “outside”), and the references are pretty quick so there is no way to gauge from this site how deeply familiar he was with Steiner specifically, but it is good to have confirmation that he at least knew of him. Also in this text, Aurobindo states his sense that his vital plane corresponds with the theosophical astral plane, and gives his general impression of theosophy.