From what I understand- any ability (weapon or class) that is within 8 meters is considered melee. HOWEVER, it gets a little tricky.
A Templar's Biting Jabs (8m range) will proc Ravager...
...but a DK's flame lash (8m range) and burning embers/venomous claw (5m range).
@ZOS_GinaBruno How about some clarification? I thought ZoS was trying to make skills/abilities follow similar guidelines.
Hidden Blade will proc viper's (i've been hit by a hidden blade spammer with vipers)
BTW Hidden blade has a range of more than 8 meters