Just about the whole film is something of a "nod" to WWI aerial combat and the romantic images of WWI flying aces.
Of course, the famous "Kessler fight" described so vividly by Waldo is based on a combination of the Voss combat with 56 Sqdn and Udet's duel with Guynemer, with "Kessler" doing the salute when his opponent had jammed guns, instead of Guynemer waving to Udet and sparing him when he realized Udet's guns were jammed.
"Kessler" coming to the US, flying in US airshows, and visiting Hollywood are all things that the real Udet did. Udet flew in quite a few German movies and starred in them as well, though he never flew in a US-produced film.
When the director and cast members/stunt pilots are screening some of the previous crashes from the filming that's already completed (using footage from "Young Eagles" and other real flicks) and the director says something like, "Here's the crash where Dick got hurt," or something like that - that is supposedly a nod to the real-life Hollywood stunt pilot Dick Grace.