When specifying a project location, D2M should notify users that UNC paths are not supported and they should use a mapped drive letter. Currently, D2M just crashes after beginning to run, requiring the user to start over again. No question really, other than why would it be programmed that way?
could be that the use of unc paths is a small portion of the user base... I suspect a large number of esri or user applications don't support unc paths directly either In fact on ArcGIS Ideas I could only find reference to UNC paths https://community.esri.com/ideas/8268 garnering a mere 100 points for SDE related