Is there a way to allow all vendors to see all media library items, and not just the ones that they have uploaded?
I understand that this seems like an odd request, but the client that I am building the site for wants vendors to be able to choose images for their items that the admin has uploaded to the media library (and ideally prevent vendors from being able to upload images themselves).
This would require that you use a user role editor (plugin) and edit the role permissions of a vendor so that they can view and edit images that are not their own uploaded images.
I do not know exactly which wp capability allows this, but it is quite possible that this will also create a security issue as the capability may also allow the vendor to view or edit other products or admin functions on their site.
Do so with caution, and we do not recommend this.