Shane... the html report is supposed to be the parameter (ie a P )
The help topic provides the requirements for the report to appear in the Results and whether it will be listed in Catalog.
If you look at the script example, it requires a path for the report, once you have set it as a parameter.
They don't cover modelbuilder explicitly, but apparently, it should be able to be done
http://desktop.arcgis.com/en/arcmap/latest/tools/spatial-statistics-toolbox/average-nearest-neighbor...