Well, I don't have a rule book handy right now, but I'm pretty sure the language says Ridden Monsters/Chariot Mounts and characters each get their own armor saves, so, following along with that, I don't think there is anything in there saying they can share a ward save; which is why the War Altar was unique among Ridden Monsters/Chariot Mounts in that the last edition Empire book said they both got the altar's ward save (there may be others out there with a similar exception written into their rules, but I can't think of them off hand).