Hello,
There is a "vendor options" section when you access the HikaMarket "accesses" menu.
Theses options are more "limitation / restrictions" for the vendor, like the minimum and maximum price he can set-up for these products depending the Joomla user group.
There is one setting for the maximum number of product image but there is no minium for the moment.
It can be an improvement for the "vendor options".
Otherwise, that limitation cannot be add via a view override, it requires a custom plugin and the usage of the "onBeforeProductSave" HikaShop trigger in order to refuse the saving of the product by a vendor if the number of image do not suits your requirements.
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.