Can I take credit for contributions to study materials on my CV? I currently work for a well-known company that publishes study materials for a certain branch of mathematics. I have done quite a bit of work under them that has been published through their website (and is used to profit the company), however, no one's particular name is labeled on the materials (they just state the company's name). 

Would I be able to include such work on a mathematics graduate school application CV other than mentioning it briefly in my work experience? If so, should I create a section "Publications" or  with some other title? ("Publications" seems misleading to me, as it suggests a peer-reviewed journal or other scholarly text of some sort.)
These are not academic publications that you can legitimately claim on your CV.  At best, you might be able to describe this work experience in a different part of your CV, but keep your publication section clean.  A publication is one that you claim authorship of the given product, whether it is a peer-reviewed article, book, book chapter, monograph, etc.  Once you have a stock of publications, then you can create some logical categories.