A certain amount of negative camber is actually beneficial in the situation you describe. As you hit the brakes, the front of the car squats, which compresses the suspension which changes it's geometry. Generally under compression, this geometry change results in positive camber, or the tyres tops pointing outwards. If the tyres were cambered negatively beforehand, under squat the tyres approach a parallel state with the road below (assuming it's level).
Designing suspension geometry is an exercise in compromise. The question here is do you want your tyres parallel with the road under compression or not. Since under compression you're generally in a situation where you're testing the tyre's grip, it seems to me that a degree or 2 of negative camber is actually ideal.