The Open Geospatial Consortium (OGC) web feature services cannot be added to the ArcGIS Online map viewer if the DescribeFeatureType operation response includes the schemaLocation tag.
Cannot reproduce problem with multiple Open Geospatial Consortium (OGC) services which include schemaLocation tags, such as:
http://services.ogc.noaa.gov/geoserver/wms?
http://services.azgs.az.gov/ArcGIS/services/aasggeothermal/AZaqWellChemistry/MapServer/WMSServer?