We do think that the CABM can be helpful for some applicants, although it's still new enough that it's hard to say exactly how much it may help. If you're coming from a non-business background and want to show that you are serious about getting a business education, passing the CABM is one way to do that.
How is it different than the GMAT? The GMAT tests aptitude, but it doesn't really test business concepts. Because it covers business concepts, the CABM shows commitment to a career in business, reveals your ability to handle rigor, and even helps you chart your course more effectively by exposing you to the full range of business concepts and helping you better explore the avenues you might want to pursue after business school.
The Association of Professionals in Business Management (APBM), the people who run the CABM, say that Harvard, Booth, Kellogg, Wharton, and the Indian School of Business "officially recognize" the CABM. At the end of the day, I can't really tell you what that means, although if there's a risk that your application may make you look like you're not serious about an MBA or that you won't "fit in" in a business school classroom, then the CABM may help you a bit.
We actually have partnered with APBM the to get a $100 discount on the CABM for all Veritas Prep students. I think it normally costs $988 to take the exam. You can learn more here:http://www.apbm.org/cabm/veritas