Hi Robert,
I am using the Application Builder and it is a Dynamic Layer. It's one of 4 feature classes that are part of the map service. Another is my Streets feature class which the labels appear. My Address Layer is the fc that doesn't label. The label is simply Address Number & Direction concatenated.
Also, on my rest/services folder, under that map service it shows "Has Labels: true" for that Address layer and it also has a description under the Drawing Info:Labeling Info
Jeremy