The Double Daggers abilities...
Bloodied Prey Passive : Your strikes cut deeper into any foe whose current health is lower than your own.
Sneak Attack Passive : Attacks upon a target's back or flank are much more likely to be killing blows.
Dance of Death Passive : You regain Stamina with every kill, the better to continue your assault.
...don't specifically mention that they're for melee only; for an archer these would be very nice bonuses to have as well, even if you have to take a few duff levels in daggers to get them.
But do they work for archery attacks?