i've travelled to numerous countries that required yellow fever immunization, including Brazil and have plenty of stamps from dodgy "yelllow fever" places, including many sub-saharan countries. over all these years, NOT ONCE have I ever been asked about my immunizations. I have it and always carry with me, but no one has ever asked me. That includes land crossings where they tend to be more strict (or at least have more time on their hands). I have US passport. In your position, I would take my chances.
YMMV