It's their high strength and fast movement which is particularly useful against dwarves. Saurus, Temple Guard, Kroxigor, Cold Ones and the mighty Stegadon all have lower or equal initiative to the stunty folk. This means that you don't want to get yourself into a long drawn out melee. You need to smash through those ranked up bearded dwarven helms in the first round.
Lizardmen are ideal for this. They will virtually always charge into combat and therefore attack first and with Kroxigor units having a strength of 7 it should be a slaughter ! The dwarf's gromril amour won't be any use to them at all (unless they have an unmodified save of 2, in which case they'll only get a modified save of 6 !)
Indeed Lizardmen are a good army against any enemy with a high armour save. They have the toughness to withstand Knight charges better than most and when they do strike back all the layers of platemail you like are not going to do much against a strength 7 hit !
Sissssssssss.......
