URL: http://mms.mongodb.com/help/faq/automation/#can-i-import-an-existing-deployment-to-mms-automation

CURRENT: Can I import an existing deployment to MMS Automation?
Yes. You can add existing MongoDB deployments to a new Automation deployment. MMS Automation will be able to manage these deployments like a new MongoDB deployment and can upgrade an existing deployment to a new version of MongoDB.

MODIFY TO: Can I import an existing deployment into MMS?
Currently there is no UI interface that allows users to easily import their existing MongoDB deployment items into MMS. Customers should start a new deployment with MMS, and then, if necessary, follow detailed steps with the help of a support engineer to migrate their existing data to the new deployment.