Service Provider - Hosting Provider definition under PCI DSS

According to Visa, service providers are defined as organizations that process, store, or transmit Visa cardholder data on behalf of Visa members, merchants, or other third parties. Now if we are a merchant and have our customer create template sites that are essentially hosted by the merchant, is the merchant consider a service provider. Again what is the key indicator that defines if a merchant is a service provider? Any insight or pointers will be much appreciated...