BLACK ROCK CITY, Nev.—The giant Burning Man art festival, in its official manifesto, calls on attendees to exhibit "radical self-reliance" as they camp and frolic on the dry lakebed here for a week every year. Burning Man's mantra is so compelling that some 50,000 participants have gathered in this rustic setting for the 25th annual rite. But some bourgeois Burners are calling upon more than spiritual vibes to tap their inner self. They've got hired help. ... Elsewhere on the desert grounds, Burners wear bikini tops, leather chaps, stilts, goggles—and sometimes nothing at all. They rely on canned food for...