Are there any brands that are / have used Vine as a marketing channel?
Or is it just a medium for entertainment related content?
What are some ways to use it for marketing a physical product based brand?
I haven't used vine myself but this article might give you some more information about the kinds of users who are successful on Vine.
Gary Vaynerchuk went one step further and created an agency, called Grape Story, dedicated to Vine stars:
http://www.fastcompany.com/3013286/gary-v-is-launching-a-talent-agency-for-vine-stars