Hi,
Yes the setting to show the main vendor in the vendor listing is only for the front-end.
Because the main vendor is a special vendor ; you can configure it in the HikaMarket configuration but there is no directly link in the backend vendor listing.
In the file "administrator/components/com_hikamarket/views/vendormarket/view.html.php" you will find the code
if(!$mainVendor)
$filters[] = 'a.vendor_id > 1';
And if you remove/comment it ; the main vendor won't be skip anymore in the backend vendor listing.
Please note that it is not done using an override but by modifying a core file ; so you will loose your modification in the next HikaMarket update.
Regards,