"Mind war" is a Witchfire power so unless noted can target vehicles such as walkers. The Psyker and the target model roll a D6 and add their LD. The difference in results determines the result. The disagreement some have said is that vehicles including walkers, are not subject to LD test, and automatically pass any LD tests.
Someone else mentioned that they are LD 10 for such things as Mind War, and others have said they are immune to it. The rule book and Errata only state that vehicles (walkers are not excluded from this) never take morale tests or LD tests for any reasons, and the person who quoted that vehicles are LD 10, could not find the reference to back their statement.
My view is that walkers would be immune to Mind War, as they never have to take any LD tests at all. Even though Mind War is a Witchfire power, it requires the target to take a form of LD test - D6 + their LD value VS the Psykers D6 and LD value.
Does anyone know where it states vehicles have a LD of 10?