Hello,
HikaMarket only consider all "Super Users" as automatic users for the Main Vendor.
Other users need to be added in the list of users in the tab "My Vendor".
I understand your need and I'll see what we can do in the future to improve that part in HikaMarket, so another Joomla group could be affected to be automatic user under the main vendor for the front-end.
For the moment, the best for you would be to add these users in the "My Vendor" tab.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.