This 2008 Washington Post — "Lie of the Jungle" by R.D. Rosen — article answers my questions:
In the fall of 2007, I had been working for several months on a proposal for the authorized biography of Cheeta, Johnny Weissmuller's sidekick in MGM's Tarzan movies of the 1930s and '40s. Against all odds, Cheeta was still alive at the age of 75, 20 years older than a captive chimp's normal life span. When the agent for Cheeta and his owner, Dan Westfall, had first approached me about writing the biography, I was astonished that a fixture of not just my own childhood, but my parents', as well, one of the most celebrated animals in movie history, was retired in Palm Springs, Calif., selling his paintings for $135 donations to thousands of far-flung admirers. His birthday parties were now covered by national, and even international, media. At Cheeta's 75th birthday party, his owner, who runs a non-profit primate sanctuary, had played a video of Jane Goodall attempting to sing "Happy Birthday" to him in the pant-hooting language of the wild chimps she had first observed in Tanzania in the early 1960s. Could there be higher tribute to a chimp than that?
I was too absorbed in the many fascinating aspects of my research -- the history of men and their captive chimps, the early days of Hollywood animal training, the evolution of the Tarzan franchise, newspaper clips about Cheeta, not to mention a meeting with the fading star himself -- to indulge any incipient doubts about Cheeta's true identity. To be honest, I was also too enchanted with what I had been told was the project's potential lucrativeness to question its premise; the agent's casual claim that she "never gets out of bed for less than a quarter of a million dollars" had worked its magic on me.