"Brown is a veteran of mountaineering films that focus on the character of climbers more than just the grandeur of the sport, and High Ground fits that mold. The director's 2003 effort, Farther Than the Eye Can See, was about Erik Weihenmayer, the first blind climber to scale Mount Everest. In High Ground, Weihenmayer returns as a guide rather than a subject, part of the team assisting the 11 veterans, plus the mother of a soldier killed in the line of duty, up Everest's neighbor, the 20,000-foot peak of Lobuche East."
More: Movie Reviews - 'High Ground' - Battered But Not Broken, Veterans Seek New Heights : NPR
According to context, I think that subject in the above text means lacking skills as a result s/he needs others to lead him/her.