I agree with boc120, I haven't seen any material that comes even close to bacta or kolto. Unless any of you have seen some sort of healing fluid. I bet that would put medics out of business real soon, so they might just keep the fluid a secret. I know I would.
Now AT-ATs are extremely tough. Quite honestly they are the most powerfull thing seen on the ground. Rancors may be tough, but they are still nothing compared to an AT-AT. A single shot from an AT-AT should be more than enough to kill a Rancor (unless it can survive with a really big hole in it's body), and the AT-AT in the game even fires 2 bolts at once. Now a Rancor is not nearly as armored as a shield generator, and in ESB, at maximum firepower the rebel shield goes down in 1 shot, and in the game, the Rancor only loses half it's health. Besides the Rancor will be kicked by the AT-AT when it comes within melee contact. Rancor on it's back, AT-AT walks on, steps on Rancor and there you have it, 1 crushed Rancor. Rancors may be powerfull, but an AT-AT is even stronger. And an AT-TE would be even stronger against one, due to the shorter legs. At some points the AT-TE is better then an AT-AT.
Besides a Crayt Dragon would be more fitting to Tatooine, the may not be as high as an AT-AT, but they are longer in the head to tail. And they are a lot stonger than a Rancor. They eat Banthas and I doubt a bantha fits in a Rancor.