I don’t know if those who consume a lot of mangoes or have grown up with mango trees around them are immune to poison oak’s urushiol(arguably much more concentrated) as its present in stems, saps, leaves, skin more than the flesh..but they likely have more tolerance.
Also..in India, we don’t burn mango leaves or branches as it increases respiratory risks..which ..now that I think about it..is likely due to the urushiol