Actually undergraduate institutions do determine likelihood of admission to prestigious business schools. Northwestern is the most represented university in both the classes in the Kellogg school of management and the Booth school of business (UChicago).
http://poetsandquants.com/2011/10/06/top-feeder-colleges-to-chicago-booth/
http://poetsandquants.com/2011/08/07/top-feeder-schools-to-whartons-mba-program/
another piece: http://poetsandquants.com/2011/08/08/getting-into-wharton-does-college-work-pedigree-trump-merit/
But these are also most trends of admitted students to these M7 business schools. You can still definitely get into a school like this from GT or UMich or UVA.