Round 1 - Rokudaime - Danzo Shimura
You did not restrict Kotoamatsukami so I will assume you just forgot to do that as this would be a non-match. With Kotoamatsukami, Kakuzu will obviously lose 1 second into the battle.
If Danzo starts with his arm sealed, he loses pretty badly.
If his arm is unsealed, he will put up a good fight, but I don't see what he has that can penetrate Domu. He will need to use his binding seal if he wants to win this, but he still faces the problem of actually breaking through Domu, not to mention the other hearts flying around trying to nuke him.
If Danzo can rid Kakuzu of Domu, he should have this in the bag with Izanagi spam. Otherwise, nothing in his arsenal can get through Domu, except perhaps summoning the Chimera elephant on top of him (if he can manage). However, considering Kakuzu survived a Bijuu slap with Domu active, I don't think it will accomplish much.
Round 2 - Godaime - Tsunade Senju
Tsunade loses, as with full knowledge, Kakuzu will avoid close quarters and rely on his Raiton Gian to paralyze her and eventually pierce her skull after she starts slowing down from too much healing. He wears her down with elemental bombardments and then hits her when she begins to slow down.
Round 3 - Yondaime - Minato Namikaze (Alive)
I see Minato winning this. Despite his lack of offense, continuous Rasengan slams should [hypothetically] eventually overwhelm Domu, and he certainly has the speed necessary to land them as well as Hiraishin. The masks are beaten easily via teleporting around the field and picking them off one by one.
Essentially, once Domu is down, it should be a cakewalk for him.
Round 4 - Sandaime - Hiruzen Sarutobi (Alive w/ elemental showings)
Pretty similar fighters here due to elemental versatility. Sandaime has the advantage of shadow clones and the Enma staff, while Kakuzu has the edge in durability and stamina. Main issue here is chakra, though. Would an alive Hiruzen have much left in the tank after using several clones in addition to elementals?
Overall, I see Sandaime winning this. Once he nullifies Doton Domu with a Raiton (which I think he can do with the help of shadow clones), he should be able to match Kakuzu's masks with clones and gradually overwhelm them and Kakuzu, assuming he does not run out of chakra.
Round 5 - Nidaime - Tobirama Senju (Alive)
I'd normally say copy and paste what I said for Minato, but the guy has nothing that can get through Domu. His "piercing Suiton" is his best bet, but Doton naturally counters Suiton, so it won't get him far. Not sure what Tobirama can do to actually get through Domu, despite the fact that I rank Tobirama far above Kakuzu on my hypothetical tier list.
If he can rid Kakuzu of Domu, just like Minato, this would be a cakewalk for Tobirama.
Round 6 - Shodaime - Base Hashirama Senju (Alive)
Loses as he did in canon.
Shouldn't even be up for discussion after we saw the Hashirama vs. Madara flashback fight. Even in base, this guy was conjuring up Perfect Susano'o level Mokuton Megazords
