Hi T D,
Thanks for the questions.
1) The ArcGIS Utility Network Management Extension was designed to be run in ArcGIS Enterprise 10.6 and above and most of the heavy lifting (edits, analytics and other good stuff) is limited to ArcGIS Pro at the moment. We anticipate further enhancements across web and mobile solutions. The utility network utilizes a new form of branch versioning which unfortunately ArcMap is unable to recognize even though the feature service is published through REST endpoints like other services.
2) The tools provided for utility network support are currently available only in ArcGIS Pro.
3) Unfortunately, ArcMap is unable to recognize the new versioning through REST services.
I hope this answers your questions.