It really depends on the school.
At some schools, the adcom is like a fortress, impervious to any outside interference (unless interference comes in the form of a very prominent alum who donated a lot of money to the school, or a prominent person who can potentially donate a lot of money to the school).
At other schools, the admissions process is a little less protected, and informal channels can work.
Alex Chu
alex@mbaapply.com
www.mbaapply.com
http://mbaapply.blogspot.com