Vendor Reviews

I work for ***, which provides software and services to help companies do webinars. I'm trying to figure out if certain companies that we use their services need to be on our Vendor Log, and if we need to perform periodic vendor reviews for them, etc. It is clear to me that our Key Vendors and all vendors who interface with our software would need to be included. But what about companies like ***, who helps us manage our social accounts? It is not clear to me where the line is in cases like this. Thanks very much.