Depends on your definition of viable, really. Is it doable? Yes. Will you lose a lot? Also yes.

You can sometimes surprise the enemy team with your ganks, but alot of junglers outgank you or just have a better clear. The only time its usable is when then enemy laners are easily gankable with fizz. You also fall behind in levels.

I would say you would probably struggle with him because his clears aren't great, which limits your options in the early game. Also the way that XP works in the jungle now, unless you get a successful gank off and share lane farm gold and XP with your laner you will fall behind solo laners in levels and gold and being an assassin from behind does not feel good at all.