Hi,
The best is to have all your vendors in the same Joomla group.
Using the "vendor registration" with "automatic creation" can allow you to pick a specific group and will assure you that all yours vendors will have the same (if you need that kind of structure).
The plugin "group filter" has been design to allow groups of users to perform the consume.
In your case, a vendor would be able to consume the serial of another vendor but it should not see it.
Otherwise, it would require a specific plugin like a "vendor filter" to not filter on Joomla user group but on the assigned vendor (the vendor related to the product which is linked with the serial).
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.