The short answer is no. Defamation is about injury to reputation. (See the Documentary Toolkit from last October 17 for more about the definition of defamation.) Reputation is injured whether the filmmaker seems to viewers to be the direct source of a false and defamatory statement (such as through narration or an onscreen reporter) or an interviewee is quoted. This is because the filmmaker is deemed to “adopt” the interviewee’s statement by making it public.
For example, if a rival candidate for mayor is shown in a local TV documentary accusing the incumbent mayor of taking bribes, and that accusation turns out to be false, the producer, as well as the local station, and the rival candidate, all are exposed to liability for “publishing” the statement. The mayor’s reputation is damaged by all of them. (Note that the mayor’s status as a public official does not by itself avoid the claim.)
Media defendants often will avoid liability under First Amendment principles if they believe a defamatory statement to be true based on sufficient corroboration, even if it later turns out to be false. A “neutral reportage” privilege also could apply in some jurisdictions. But the mere fact that the rival candidate is shown onscreen making a false and defamatory statement does not absolve a filmmaker of potential liability.