So, thoughts about ZAC. He doesn't seem viable at all outside of jungle. He's like...a melee Cassiopeia. His DPS is good, but he has horrible burst, and he can't even just toss up some DoT and walk away like Cass. He's also heavily dependent on the slow on his Q and his victim not having any escape or movement cc (escape on CD is not good enough unless it's like 20 secs), since that that and his ult are just about the only reliable cc he has, and his ult has like 2 mins of CD. His stun is usable, but it requires charging up, doesn't stun very long, and is pretty jukeable. Even with his passive, in fights vs other champs unless he aims to just bounce around a teamfight just generally AoE'ing everyone nearby, his skills still do a good job dragging his health down as he won't have the luxury to just recollect his droplets in the middle of a fight. His reforming passive only seems to be good for deterring tower dives and giving him a second chance in teamfights where his team is winning, as it's really easy to kill the globs, and they're uncontrollable. He's not really a good pusher either, as he is easily kited if he tries to chase anyone out of his lane, his AP ratios don't help much with killing minions, and he's just generally a really shitty champ to build AD on.
As for being a jungler, in my opinion, he has just about perfect sustain, but I can't really see him being able to fend off invaders or win duels without the enemy jungler just simply deciding to steal his big creep and leaving or just punching him out. Being a melee AP (D:) he can't get much use out of red either, outside of for killing creeps (and he's still better off just giving his ADC red or just ward it and gank enemy jungler when they show up to take red). Using red to slow down enemy champs for ganks doesn't really work if you're underfarmed compared to them, can DPS but can't burst a lot, and your main non-ult method of damage involves sacrificing your health continuously.
So my 2 cents. Though I rarely jungle, so consider my thoughts on jungler ZAC at your own peril