Couple of initial thoughts, and questions as well:

1. Do you care about the PvE aspect of this combo at all, or are you only interested in PvP?
2. How do you plan on leveling post 60? Are you going to use one (or both) of the druids as your tank(s) post-60?

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This might be kind of bias since I'm running a 4-shammi + 1 pally team, but here it goes anyway :twisted: : The Paladin will give you the ability to tank an instance, no problem. Depending on how you spec the Pally (Holy or Prot), you can compensate for the heals, or just give your entire party great armor benefits. With the shaman, you can put down a tremor totem (fear immunity at your whim), you also get unlimited health regen from the shaman (healing spring totem stacks).. And you'll get Chain Lightning for PvP, plus Chain Healing... Your chain lightning combo off of 4 shammis will be enough to outright kill any single player if you cast it on that exact player at the same time, ideally it should kill 2 players at a minimum, leaving the third badly injured (once you get your gear up).

But, I could go into a whole different discussion about shammis, so lets get back to you...

Warlock pets aren't going to be able to handle high level instances as a "main" tank. They're awesome for PvP, but in a PvE situation they're going to be excellent until around level 60, then you'll notice things start to taper off when your pet(s) are getting hammered. If you don't care about the instances though, then your Druid + lock combo should be viable.