As I'm a Skaven player, I have a few options to deal with ogres. First off, ogre gunlines don't scare me at all. there is no way they will kill enough rats to affect my strategies at all.
The first and foremost tactic is to run slaves. Lots and lots of slaves. Not only will they soak up all the fire, but they will keep the ogres locked in combat while I lob Poison Wind Mortars at them. Boy do I love weapons that ignore Toughness and Armor saves!
Options two and three come from the Skaven spells of Plague. Wither is a big help in dealing with ogres, as it can permanently reduce the Toughness of the unit, making them far easier for my rats to wound. Additionally, Bless With Filth will give a unit poisoned attacks, so even the slaves that are acting as a quagmire can do some potentially serious damage, especially if I also manage to cast Death Frenzy, giving the little 2 pt buggers 3 poisoned attacks each.