"Hallucination" is one major stylistic device used in association with Willy's view of the American Dream in the play. While Willy does speak with Charley about what it takes to get ahead and succeed, the greater articulation of his vision of the American Dream is carried out during his episodes of flashback and delusion.
Willy discusses success with Ben and Willy's own definition of success is symbolized by his brother. This symbolism works in two ways. First, Ben's history and his character are examined. Ben is bold. He takes risks. He gets rich. He is a "great man". Second, he appears as an apparition, a figment of Willy's delusions. Ben is a dream, literally.
These qualities (of success and fantasy) are paired so closely as to become related. In this way, Willy's view of the American Dream is implied to be grand but delusional through the use of the device of the hallucination.
In addition to this stylistic device, repetition is used. Willy repeats his mantras of success and in this way demonstrates his fixation on an idea (an idea of questionable reality).