Killing Karador without losses is very easy - more so then killing Haas this way!
The trick is to keep him from casting harmfull spells at your units, as he has a wide selection of those (Fear, Hypnotize, Fire rain). This can be easily achieved by killing one of his stacks every round (Bone Dragons are likely candidates for this). Assured that you kill one stack, he will always cast Necro Call on them.
I beat him by having Lina cast Ice Shards in the first or second round - the AI is often very dumb, and his Death Knights kept hacking the shards for 3 rounds, by the time they got through I killed all his other units.
Try to stand on the corpses of the heavyweight units (knights, Necros) to ensure he or Karador's crystal doesn't raise those - Totems also work fine. Just be sure you don't destroy the corpses!
Then, when all his units are dead, I used the reliable "Superchargers + Resurrection" combo for at least 20 rounds to resurrect all my losses. I always made sure to have at least 5 Rage in reserve, and when I ran out of rage to cast Superchargers, I "stepped off" of a skeleton or Dead Spider corpse, let the crystal raise it, then - before giving it a turn - casting Rage taking on it.
This way, I had no losses at all. Just remember not to let the raised unit get a turn, or Karador will go whupass on you with spells...
For the record, I was playing a Paladin and my troops were: Black Dragons, Royal Snakes (my killer stack with Snake Ring and frog Fiona as a wife), Black Unicorns (I only used them against Undead, I use Evil Beholders otherwise),Griffins (with banner of Griffin I had around 450 of them at the endgame). Of course, I also wore items to help me against Undead (Silver Sword, Holy Shield)