It depends. In most Nibelungen texts, he doesn’t encounter a dragon, but rather a long lindworm with shiny armor.
In these accounts, someone slays the lindworm, but not through direct combat. Instead, he uses an invisibility cloak, takes the creature's treasure, and bathes in its blood. Later, he meets his end due to treachery. Clearly, this is a work of fantasy.
But what about the Roman historian's lament regarding the Battle of the Teutoburg Forest? Over 150 years later, and they’re still singing his tale... the song of Hermann the German. Unfortunately, that song hasn't survived. However, the Nibelungen texts remain, where Siegfried (Hermann) defeats a long worm with shiny armor (symbolizing the Roman legions), not through open battle but by ambush (the cloak of invisibility), seizing their treasure (the dragon’s hoard), and ritually killing their leaders (bathing in blood). And, just like Siegfried, he is ultimately undone by treachery.
The parallels are so striking that it seems highly unlikely to be a mere coincidence, especially since Roman writers noted that "his song" endured for an exceptionally long time. The Nibelungen texts IS THIS SONG!
I say the Nibelungen Tale is based on facts. And the same may be the case with Atlantis.