Jobs, how would behave in this Physic Scenario?

I would like some advice here: it seems to me that a scheduled ICollisionEventsJob will be executed in parallel, for each collision I guess (please confirm)

in our job implementation we got these fields:

Code (CSharp):

1. [NativeDisableParallelForRestriction] public BufferFromEntity<CollisionEventData> CollisionsFromEntity;
2. [ReadOnly] public ComponentDataFromEntity<PhysicsVelocity> PhysicsVelocityGroup;
3. [ReadOnly] public ComponentDataFromEntity<PhysicsMass> PhysicsMassGroup;
4. [ReadOnly] public NativeSlice<RigidBody> Bodies;
5. [NativeFixedLength(1)] public NativeArray<uint> idCounter;

I guess I could mark the first one as read only instead of NativeDisableParallelForRestriction (which worked), but what would the effect of the last NativeArray be? Would writing in it force everything to run in serial instead of parallel?