A provider is the content owner in direct contract with iTunes. An encoding house is contracted by providers to create metadata, encode content, and deliver content directly to iTunes. Encoding houses do not have a contractual relationship with iTunes. Note that the same company can act as a provider and an encoding house.
The provider account is for iTunes Connect and day-to-day use. The encoding house account only works with Transporter.
You may have two accounts if your company acts as a provider and an encoding house.
To set up an encoding house account, create a group email address that includes everyone in your company who will use the account. Provide the group address to iTunes by using the Contact Us module on iTunes Connect.