Unfortunately there’s no way for me to know how your multi-vendor plugin processes its vendors, but since you are sure that it’s not the meta data, it’s easy to check whether they are registered as custom product taxonomy: just search the Add filters dropdown located in the Filters section of your preset for anything that sounds like vendors!
If your multivendor environment uses some kind of proprietary registration format, then it’s definitely not possible to make a filter out of it. Our filters only support the native WordPress / Woocommerce hooks and procedures.