Actually, you can even do 9 daily quests for them when you are rank 3. Furthermore, max rank for the initial 4 beast tribes is 4, while max rank for the Ixali is 7 and max rank for the Vanu Vanu is 8.
There is a way to bring every tribe reputation to 8 (i.e. the initial 4 and the Ixali) but it is not related to spamming daily quests.