While playing as Mvemba A Nzinga, the Religion tab does not appear at all. This may be due to the fact that this leader can not start a religion, gain great prophets, or build holy site, and it is an issue. You are still affected by the major religion in your cities, so should be able to see the beliefs of every religion as it may dictate how you interact with other civs or use apostles that you gain. It's not that something was missed, so it seems strange that Firaxis would take out the religion tab for this leader/civ.