That would give Kakashi and Darui a significant advantage (I'm not stating that's wrong, just stating a fact). At that point it mostly boils down to how effective Kamui would be against Sasori's core shift and the Third Kazekage's iron sand. However, the terrain give Kakashi and Darui an even greater advantage since Sasori needs to be able to see where his opponents are in order to make good use of his puppets. Another big factor for me is how capable Sasori is at flying. He only displayed this ability for a short time, but he appeared to be fairly aero-dynamic and fast.
With Kakuzu, actually having all the masks merged within himself would be a massive tactical error in this case due to all of the possible hiding places. Unlike Sasori's puppets, the masks can act independently of Kakuzu's will. I would like to think that his vast experience would tell him it would be foolish to completely merge with his masks under these conditions.
As far as Darui goes, I find him relatively hard to evaluate. It will be easier once he gets more anime time - it's hard guaging abilities strictly from the manga. I would like to know what elements make up his storm element. A reasonable guess would be lightning and water since those are his other two elements, but it isn't for certain. I also can't evaluate the weaknesses of his jutsu since it's a bloodline limit, making it much tougher to analyze since you don't know how it reacts to other elements.
If we take one last look at the terrain you set, again it does put Sasori at a bit of a disadvantage unless he and Kakuzu destroy the surrounding cover. If they did that then they would regain the advantage. They are also both long-ranged users while Kakashi is a close-mid range user (he is leading the close-mid range squad) and Darui is a mid-range user (leading the mid range squad). However, a big part of fighting in a rocky terrain is sensing abilities. Kakashi has smell (which would only work on Kakuzu since Sasori theoretically shouldn't have a scent), Darui and Kakuzu don't appear to have any sensing ability, and there was only that one instance where Sasori blocked Naruto's shuriken that he displayed any sensing ability (I can't accurately evaluate his based on such little info.). As far as sensors go I can't give either group a huge edge.
Regardless, under the conditions you set Kakashi's and Darui's odds of winning go up. I'm not saying they would be able to win 100% of the time, far from it actually. But their odds would be better than what I initially gave them. A good portion of Kakuzu's and Sasori's strength comes from the secrecy of their techniques, so letting Kakashi and Darui know their abilities evens things out much more for me. There are too many unknowns with Darui to give a definitive percentage, but I'd still say Team Akatuski has enough sheer firepower and stamina to win more than 50% of the time.
