GeoServer 2.11.1 Windows 10 SQL Server 2016
To retrieve feature type info, one of the executed queries calls sp_columns_100. This means that for the column containing geometry data, it will receive geometry.
It would be an improvement to call the STGeometryType function on the column, to determine a more specific type like Point or Polygon.
This in turn would allow GeoServer to automatically apply a proper SLD instead of falling back on a default SLD.
Example of a feature type loaded via an SQL Server datastore:
Example of the same feature type loaded via a shapefile datastore:
As you can see, the shapefile datastore correctly determines the MultiPolygon type, while the SQL Server datastore simply uses Geometry.