He gets an equal increase to his damage from Aim and Cunning; as in: each point in Cunning will give him 0.20 DPS and each point in Aim will give him 0.20 DPS.
However, in an ideal situation you would use both stats. This, because a main stat also gives additional crit chance, however this is on a diminishing return scale. What this means: 700 Aim + 700 Cunning = same amount of raw DPS, but more crit chance, than 1400 Aim and 0 Cunning, for instance. Try to balance out both stats for maximal returns.
Great post, my compliments.