Our only in-game-recorded instance of Morihaus appearing was the slave rebellion with St. Alessia (1E 242). The Ra Gada didn't invade until some time later (1E 780), yet the new furnishing package has a 'Ra Gada Guardian Statue, Winged Bull' in it. Given that the Redguards conquered or fought almost everyone they came into contact with and about half of their society scorns Imperial culture, I find it unlikely they got that depiction from the Imperials. So when did Morihaus visit Yokuda, or otherwise make himself a prominent enough figure that they started putting statues of him in their tombs?