Hi Mayank,
Yes there's a definite weightage given to Work ex in sibm , scit.. they spell out the percentage that is alloted to the written exams, academics, gdpi and your work ex....
( not sure about MAT colleges)
What I would suggest is -- search for the forums dedicated to snap/sibm/scit/mat colleges..
here's the link for SIBM related threads..
http://www.pagalguy.com/forum/tags/sibm/
Hope this helps you
Cheers
Abhirup