Early in his career Nelson did stunt work for B-movie producer Roger Corman on the films "Swamp Women" (1956), "Attack of the Crab Monsters" (1957), "Rock All Night" (1957), "Carnival Rock" (1957), "Night of the Blood Beast" (1958), "The Cry Baby Killer" (1958), "Teenage Cave Man" (1958), and "A Bucket of Blood" (1959). In 1958, he acted in and produced actor-director Bruno VeSota's science-fiction/horror movie "The Brain Eaters", with Roger Corman as the executive producer. The same year, he was cast as the lead in "Devil's Partner", but the movie was not released until 1962. He also appeared in the 1960 thriller "Valley of the Redwoods" and the 1963 comedy drama "Soldier in the Rain", starring Steve McQueen and Jackie Gleason.