Yup I agree, I also mentioned that on some thread but it got totally ignored.. it's about the fact that (why Kabuto didn't let Nagato to absorb Amaterasu), but instead.. he used Shinra Tensei to blow it away..? that's a prove that Amaterasu "can't" be absorb, neither is Susanoo.. Amaterasu used to be called the flames of "Hell" or something like that, has anyone forgot? yes it's made out of Chakra but I also think it's something special..
Also, Kabuto isn't stupid.. if Amaterasu could have been absorbed, he would've absorb it to let Nagato regenerate his health, so that he would recover to his original statues, but instead he used Shinra Tensei to blow it away cause he COULDN'T absorb it.