It depends on the species of cray but right now some of the rift lakes are having a plague of imported louisiana red swamp crayfish so at least some adapt very well.
They don't mind a high pH. Generally speaking it is ok to keep crayfish in a pH range of 7.2 to 8.4. The colder the water the species comes from, the higher the preferred pH. is, However anywhere in there will do just fine. It is relevant to your kH and general hardness (calcium). Keeping both of them high will not cause any issues with your crayfish.