Barrett focuses on GPA and Test Scores only when you have good ones. When you might be a little on the low side, that's when the other things come into play.
As a recent graduate of Barrett on my way to medical school, I'd be more than happy to send you a message detailing my experiences there. Just PM me if you want it.
As far as undergraduate affecting your medical school, that really isn't true so long as you go to a school with enough opportunities for you to excel. What you do is always more important than where you go when you are in a meritocracy like medicine. You will find that the benefits that Barrett gives students at ASU is an enormous competitive advantage in the medical application cycle. In my medical school interviews, a few schools were interested in the BHC, but most of the focus was on what I had done. How the BHC helped me do it was of interest only to the point that I could make comparisons between my love of Barrett and my desire to go to the school in question.
Also, here is my blog (which doesn't discuss my BHC life). If you go back to the original posts you will find a lot of helpful hints and tips
Med School for Dummies