Hello,
Depending on your theme and how they hook the theme header in will determine if you can disable that on the shop pages for the vendors. If your theme does provide this, then you can load and unload the filters we use to hook into the shop loop. You’d have to talk to your theme developers to see if that is possible. Based on the screenshot you’ve provided I don’t think it will be possible, but can’t hurt to ask your theme devs.
We use the woocommerce loop actions and filters to display our header above the products.
cheers,
Jamie.