Applying to Demand

I'm in the process of applying for work at Demand Studios and thought I'd ask here since there seems to be a lot of accepted writers on this forum already. I'm rewriting my resume to include experience relevant to the general area covered in my sample writing piece. The sample writing I'm including covers aquarium maintenence, so I'm including a "Niche Experience" section in my resume stating years of experience in different areas of aquarium care (and other animal care), and omitting most of my work experience except for a position in Aquatics at a pet store. Is this the way to go about applying, or should my resume be much broader? I don't really have any professional writing experience, so I'm hoping to let my sample stand alone and use my resume to build up my experience and knowledge in an area I'm comfortable writing in.

Thanks!

Edit to add: Would it be overkill to include a letter of recommendation from a recent employer and a cover letter within the resume document?

Thanks Ken, that was helpful.

I applied and was rejected, but I think the writing sample was in the format that they were looking for. It was a how-to article, about 450 words in length with an introduction, 5 steps, 2 tips, and 3 print sources cited. I began each step with an action verb and wrote concisely. I'm guessing that the reason I was rejected is that my topic was too in-depth and maybe I didn't explain the obvious (to me) things well enough. My topic was "How to Cycle a Freshwater Aquarium with Fish". A lot of people who keep fish don't know about cycling, or don't know that there's a difference between fishless cycling and cycling with fish. I might try writing an article on a different aquatics-related topic and see if re-applying changes anything.

Thanks for all the replies, I appreciate your time!