True, but you never know. Alucard may have inherited this and it just changed, like an adaptation or something.
Otherwise, maybe Yoko uses her magic to forge Alucard a disguise. After all, she knew who he was in Aria of Sorrow, when she met Soma and asked if he had met "Aluc-I mean, Genya. Arikado, right?" Plus, in Dawn of Sorrow, she could've easily changed him back as soon as they left the castle considering she was with him. That's probably more likely.