I have jungled many AP casters, such as Lux or Brand, but I find that Viktor is great at jungling because of many reasons:
-He's tanky for a mage
-Good CC for ganks
-AoE and Shield

Viktor is a tanky mage (Well, at least how I play him). I play him like I do Swain, I build a RoA and Rylai's. Health never hurts, and when you have 800 AP late game, you can still hit VERY hard.

He has good CC. His W skill, Gravity Field, is great in the jungle. He can stun camps with it to reduce his incoming damage. For ganks, he can lay down his field like a Trundle pillar and block off the enemy, or place it right on them for the inevitable stun. He can cast Death Ray as he runs to the victim since it can be cast on the move.

Viktor's AoE helps him in the jungle as well. The Death Ray can hit all of the jungle minions very hard. The shield helps in the jungle to reduce incoming damage on all the monsters. It helps a bunch.

Surprisingly, Viktor jungle is strong, I've done worse.