Hi,
The "vendor select field" created by the plugin "hikashop / market_vendorselectfield" (I didn't find a short name for it), is using the HikaMarket Vendor selection type.
It means that it is the same code used when you want to select a vendor in the backend (to assign a vendor to a product, to filters a vendor on a listing, etc) and in the front-end for the custom fields.
The best will be to split it into two different types so they can have they own "life". The current type works good for the backend and for the filtering stuff, but the front-end part, for the custom fields, requires more features and more parameters.
Regards,