In the Churning Mists, there's a statue on a solitary island near Moghome called Statue of the Unsung, which (according to the sightseeing log) bears the inscription "along with the memory of thine heroic sapphire wings" in early Ishgardian letters.

And considering there's only one blue dragon we've seen thus far:





It looks like it was erected for Nidhogg? If so, it seems to hint he was at one point fairly close to the humans, or at least helped them.