What menu area it uses is probably defined in it's [ADDON]/schemas/menu/menu.post.php file and should be able to be easily changed.
Most likely the template you're interested in is:design/themes/responsive/templates/views/companies/view.tpl
You would use thehook 'companies:tabs' to add additional tabs to the page.
A vendor's products are shown using the products.tpl template in the same directory.