Hello Mike,
Think of the certification exam as a credential and the cattle drive and experience. I was skeptical at first about the cattle drive, but after simply submitting 1 assignment, the code review is very rigorous. This has forced me to stop, think, think, and think some more about what I need to do and how to elegantly solve the problem in accordance with the style guide. I highly recommend the cattle drive and look forward to learning good habits along the way.
I don�t think the cattle drive will help you much with the exam since the exam is very tricky. Passing the exam is about burying yourself in exam prep material for weeks until you are savvy to the ways of the exam and are able to consistently pass the practice exams.
Good luck!