The only thing is that after Kakashi forgave him the White Fang was able to go into the Pure World, as he said, to be with his wife. That was during the Pain arc, but Kabuto didn't raise edo tenseis until after the Pain arc. So if he had wanted him, and had already gathered DNA from his corpse, he would have been able to bring him back.
but kabuto didnt know that and by that point it is very likely he had already tried and just gave up on sakumo.But Sakumo eventuality passed on after his talk with Kakashi.
The juubi tree is the tree he sowed.