There's some good advice in this piece but the tone is a little off.
It almost starts from the premise that you're at a disadvantage and goes on from there to help you counter this. I think this is an inaccurate way to present things and in many cases actually the opposite of the truth. That may be true somewhere like Wharton, but at most other schools I really don't think that's the case.
The 'quant stars with Wall St experience' are solid b-school candidates but when you get to the rarified heights of the top schools they can struggle to stand out. Interesting 'nontraditional' (that term needs replacing ASAP) experiences have the benefit of, in many contexts, standing out immediately. I also find that many people who have worked in 'nontraditional environments' often have much stronger leadership skills than their peers in mainstream companies, are much more comfortable with ambiguity, more rounded people and more resilient. In many cases people have had experiences where they couldn't rely on formal structures, were in less bureaucratic situations and had to call on personal resolve and skills that are not tested in a highly structured environment. Many schools and many firms rightly value all of these things.
I suspect that the author of the article would say that they acknowledge this, and indeed some of these points are in there. But at the same time the tone is not as positive as it should be.
My main advice to nontraditional (okay, I'll drop the quotation marks) applicants is one thing and one thing only: don't sell yourself short. Your experiences are more valued than ever before (and not just for 'diversity' - a slightly patronising way of putting it), and you have a place at the top programmes waiting for you if you can show the skills required to be successful in business. The advice in this article is a good start, but don't be cautious about it and definitely don't go in there believing that your experience is less impressive or less relevant than your peers', simply because it is nontraditional.
Cheers