When you add an account to Outlook, your mail, calendar items, files, contacts, settings, and other data from that account will automatically sync to your device. That data will also sync to Microsoft servers to enable additional features such as faster search, personalized filtering of less important mail, and the ability to add email attachments from linked file storage providers without leaving Outlook. You can remove an account or make changes to the data that is synced from your account at any time from within the Outlook app.
When you set up your Surface Duo for the first time, you are prompted to sync your contacts between Microsoft Outlook and the Google Contacts app. If you turn on this feature, your contacts will be maintained in both locations and any changes will be reflected in both apps. All Outlook functionality will work regardless of whether or not you choose to sync your contacts with Google.