Thanks for weighing in and pointing out what I had missed in that documentation page. I appreciate that.
From a security perspective, staging and production are treated equally, so my concern for the duplicate Account and Contact storage isn't as much about security in this instance as it is about the the principle of not having to maintain the same data in two or more places via a manual process.
I'm curious what Kentico's expected operating model is for Contact Management (Contacts, Contact Groups, Accounts, etc.) and Email Marketing in a staging + production configuration. Kentico's stated preferred container for subscribers for email campaigns seems to be Contacts and Contact Groups, but these do not sync. Email Campaigns and Email Templates do sync from staging to production. If you create an Email Campaign in staging, but do not have the Contacts and Contact Groups in staging, you would not be able to set Contacts or Contact Groups as recipients. This leads me to believe that either (a) Kentico intends for you to manually maintain Contact and Contact Group data in staging and production, or (b) Kentico intends for you to perform all Email Marketing activities on the production server only.
Two other thoughts come to mind:
1) Perhaps they intend you to perform all Email Marketing creation on staging, then sync it to production, and then perform scheduling directly on production.
2) Bi-directional sync'ing might also be a more complex way of handling a option B above where you create the Email Marketing campaigns on production and then sync them back to staging
I'm curious to hear what Kentico's ideal workflow is for email marketing with EMS in a staging + production configuration.