I have seen no evidence of the kuhlis attacking the shrimp, just them pushing through the shrimp in quest of food.
I put a few of my RCS in with the kuhlis earlier this year, and noticed an increase in the population within weeks. They compete but the shrimp are holding their own and more! The kuhlis mainly eat off the bottom, occasionally snake their way through the plants as they forage. The RCS eat off the bottom, and in the plants, too, but also are all over the two sponge filters.
I did notice a brownish shrimp, a throwback. To prevent him from fathering more browns I'll cull him soon.