I'm pretty sure I made a post here related to this subject, but I would hire a marketer that knows some design over the opposite if the purpose of the site is to make money. There are sites that are not intended to make money such as a dental office that is always booked or some corporate sites.
I would want someone to come up with site site structure and layout from the marketing side as well as the basis for
SEO ie domain names, page titles, keyword research.
They can farm out graphics, artsy stuff, scripts, and copyrighting. I would expect them to edit the page copy for
SEO.