Is Nocturne too weak for the jungle?
It is just a feeling. I play Xin Zhao and he can clear his whole jungle and is full health with 2 potions. Twice. I play Shyvana and she can clear her jungle with more than her half health bar. And fast. I play Volibear and he can clean his jungle with 50% health (without using his passive).
I play Nocturne and die by the wolves.
Is it possible to double his passive bonus when he hits a jungle monster? You did something similar with Volibear (50% cooldown reduction if he bites a monster) and I would be glad if he is able to survive his early jungle clear, too. 
Just this one buff. More do I not ask. :(