[13lackGu4rd]

well, Dawn Guards are perhaps the best regular(as in non sacred) infantry unit in the game. however, this doesn't mean they're invincible. there is no way you're troops "cause no damage" as Dawn Guards only have 1 protection. they do have 12 defense and 25 hp though, which means that you probably just don't have enough numbers to finish them off during the battle. Dawn Guards are size 3 which means that they can be swarmed by size 2 troops(basically all your troops).

so the key to fighting Hinnom, and any other giants for that matter, is to have superiority in numbers. but, if you also care about your own troop composition than your Elite Warriors will be the best match for them, with their 12 attack skill, but really any of your troops will work. just have enough numbers and script them properly and you shouldn't have any trouble against them.