Hi,
The "Joomla user id" is stored in the HikaShop user table ( user_cms_id ).
HikaMarket store the vendor administrator under the column "vendor_admin_id" ; the value is pointing to an HikaShop user id.
In the table HikaShop user ; you will also found a column "user_vendor_id" in order to link a user to a vendor.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.