FYI, I'm still in the process of implementing this process, but here's my plan right now
1. Use FME server to update the feature classes on the second sde at night. (it is less finicky than replication and doesn't require the datasets to be versioned. You can tell it to compare an ID and whatever other fields you want to identify inserts/updates/deletes and make the appropriate edits.)
2. After the feature classes are updated the tables that drive the geometric network on the target system will be invalid since FME doesn't manage those. To fix this, I am writing an ArcPy python script that will run afterwards. It will temporarily version the target dataset, , run the repair geometric network tool, run the set flow tool, and then unversion (check option to compress edits in DEFAULT to base).