Doesn't the Final Summon cause the Summoner to merge with his sacrificed Guardian...there aren't any fayth statues of the guardians anyway in the world, so that's why I'm thinking this.

But Anima is just a normal fayth of a sacrificed human, just like all the other fayth around the world. This one just happens to be Seymour's mum. Although, why on Earth she thought it'd be a good idea is beyond me.