I believe assassin should be able to use any type of weapon but benefits more on melee weapons. Considering the attack speed of the weapon I think it would be better if it depends on the build.
In terms of ranged weapons I think assassin should be able to use deferent type of grenades, I have never seen a tap target mmorpg launching flashbangs that loses enemy target and blind the enemy player screen for a while. That way assassin would be able to use different type of grenades like smoke grenades, flashbangs, fragmentation grenades, glue grenades. But I don't know if should be an item, skill or weapon.