Amaterasu is faster, so Madara can one shot Kakashi faster than Kakashi can one shot him. Let us be realistic, Kakashi is not using Kamui at the very beginning of the fight. And since Kamui is not instant but takes a little time to absorb objects, Madara will have enough time to act. And if you think that someone who combines the EMS, Rinnegan and Mokuton can't use a reasonable counter, you must be naive.
And I don't know if Kamui is working on Edos after all, their soul are bound to the world and we don't know if it is going for other dimensions as well or for the humans only, so an Edo Tensei will always appear again since his soul is bound to the earth.