Is Shinsuusenju a summons?
According to Naruto Wiki Hashirama creates the statue using sage art wood release: true several thousand hands technique.


  After entering Sage Mode, Hashirama creates a wooden statue of titanic proportions


Link http://naruto.wikia.com/wiki/Sage_Art_Wood_Release:_True_Several_Thousand_Hands from the comment of @HappyFace .