Ulysses is inspired by the Good Shepard and a character named Cowboy. His flag pole is not a weapon per se, but his shepard's staff; he wears his flag on his duster. He's got a Rastafarian vibe, but that could be aesthetic - something to draw our attention, to set him apart as oddball. I'll wager the graffiti in the canyon is his, and Ulysses is inviting the Courier "home."
The OWB teaser's "even greater threat" may be ODYSSEUS. Someone has driven the robots hostile. I doubt the Think Tanks would coerce the Courier to do a job for them, then throw extremely dangerous machines in his face.
Though I'm thankful for its inclusion, I'd like the Big Empty to be unlocked in stages, like Tibbets' design. And just maybe Ulysses will briefly ally himself with the Courier. Or, as others believe, he's left recordings, which will make helpful allusions to the quest line and OWB's locations.