On our Balto test mule I noticed that the "ROOT" application that defines the robots.txt service works as expected.
Root service here: http://balto.opendap.org/siteMap/smap_0.txt
Returns (correctly):
But the Hyrax endpoint here: http://balto.opendap.org/opendap/siteMap/smap_0.txt
Returns (incorrectly):