The plagues of unemployment, alcoholism, and violence that ravage the Pine Ridge Indian Reservation in South Dakota are as starkly visible as the monumental carvings on nearby Mount Rushmore in Skins, an angry drama about the bond between two adult brothers on divergent paths. Mogie (”Dances With Wolves”’ Graham Greene), a thrice-wounded Vietnam vet, rots from drink. Meanwhile, his younger brother, Rudy (”The Last of the Mohicans”’ Eric Schweig), a tribal cop, curdles from bitterness that drives him to acts of vigilantism. Directed by Chris Eyre and shot entirely on Pine Ridge with no time for any of the charm he varnished on ”Smoke Signals” four years ago, it’s a rough, ungainly thing — something of a Frontline documentary scrambled with a clunky family melodrama. The fury and frustration are authoritative, but the unsteady technique of the storytelling weakens our ability to feel the full intensity of the filmmaker’s despair.