Not sure about the damage you deal but I believe it only affects ranged weapons. However, I do know that you take more melee damage if you are in aim mode. Always a good idea when engaged in melee to stand up.
For the time being, you can see the effects of aim mode as the "Crouch" passive on your character status screen. (The "Other" section is being removed in S2.)
Sadly, it doesn't definitively answer the OP's question. Even though most of the effects are "All damage +XX%", there's an asterisk next to each one meaning it's conditional. But as everyone else has noted, the condition is probably "for ranged damage only."
The -100% melee resistance was an eye-opener for me, didn't realize it until very recently.