First of all Kisames only Chance not to get completely obliterated is using his Waterdome righ off the bat (what is unlikely but...). None of Kisames attacks can kill Hidan and no attack can get past Kakuzus Skin so the only Chance for Kisame to kill Kakuzu would be drowning him in his Waterdome. If Kisame decides to Encounter them at Close combat he will be dead very very fast (reasons should be obvious). Then back in the Waterdome i just cant see an extremely powerful Shinobi like Kakuzu drowning, he will release his hearts fast and maybe he can even move out of the dome with the help of his masks and tendrils, plus Hidan surely will distract Kisame in Close combat. Then Kisame just cant absorb, or block, or whatever, when Hidan engages him in Close combat and Kakuzu fires his elemental blasts from all directions, Kisame will die after a heavy fight, but in the end he cant really hurt Hidan and Kakuzu so they win low-mid diff.