HOLLYWOOD — Monday night’s pre-show reception for the 3rd annual “Backstage at the Geffen” benefit got the thesps in the mood for the skits to come later in the evening.Honorary co-chairs Christine Lahti and Tommy Schlamme said they loved the chance to help their “neighborhood theater” — and pal Gil Cates, Geffen’s producing director. “Gil Cates is a friend — whatever he wants,” Schlamme said. Lahti cast the Geffen’s relationship to the Music Center downtown in New York legit terms. “The Geffen is more like Off Broadway and the Ahmanson is like the Lincoln Center,” she said. Monday’s benefit, which honored Karl Malden, raised $205,000 for the Geffen, which is about to undergo a $25 million renovation.