I don't think Viper Sting / Mana Tap is a serious threat to Jaina Zoo. First, it's a debuff. What that means is that you won't want to kill whoever you're putting this on prior to tick 11 (and with Jaina, maybe not even after that, since you want to turn off GWE shenanigans). Second, Mana Tap? It's 2 range. Unless there's a Blood Elf Warrior I don't know about playing Breakthrough, there's almost no way you're getting in 2 range of Kaustron or Jaina with pets blocking your way (and yes, I know they don't block you walking through them, but having a bunch of them two deep stops you from moving in range).
Putting Viper Sting on Kaustron just means you're safe from having him cast a pet just to have a double pet team up on the same turn (since they won't want to waste a pet card that won't ready back). Unless you take time to kill the pet, or kill Kaustron (in which case he loses the debuff), that's not going to put much of a damper on him.
On the flipside, it's a decent answer to Goblin Fog, and the threat of it showing in sideboards will stop ME from trying to top 8 with the Goblin again. :)
"The beatings will continue until morale has improved."
- Standard corporate management technique