UPDATE: A quote from the production notes regarding Tom Waits' appearance:
During a key scene at the end of the second act, the audience is suddenly introduced to yet another character, `The Wanderer,' played by singer/songwriter Tom Waits. He appears in the desert seemingly out of nowhere, similar to the role of the chorus in a Greek tragedy.
"The Wanderer explains a lot," says Scott. "Basically, he gives a summation of what's happened up to that point in the story. He also seems to have a psychic connection with Domino but no one knows if he is real or simply a figment of the imagination."
Scott and Waits discussed the origin of the character and decided he would be a gun toting, Seventh Day Adventist sporting a bandaged hand. He also foreshadows what is about to come.
(Source: Domino official production notes, 2005)
Thanks to Pieter