There is a problem with running hordes vs ogre gun line and that is simple that they can take 200 noblers and 24 leadbelchers supported by cannons charge knoblers take all there stand and shoot fire and dt tests plus hq with an amazing majic law
However this plan has one HUGE flaw. Gnoblers have atrocious LD values and without a BSB the chances of Gnoblers runnig off at the slightest loud bang is rather high.
My armies are both Tomb Kings and an all plague Skaven force (I also have a small amount of Chaos but since I have not used it much I can't really comment).
My Tomb Kings suffer against Ogre gunlines. Mainly because it is Chariot based which limits how many men I have on the table. However in the Tomb Kings list there are plenty of options that either can render the gunline moot (such as a huge 40+ man block of Skellie Archers with Khalida for poisoned arrows) or units and spells that force initiative tests (which Ogres do not like) such as Sepulchral Stalkers, spells from the Lores of Death or even units which can either get their very fast (skellie horsemen) or even are tough enough to get their in one piece (Necrosphinxes). Additionally it may be wise to invest in a small unit of Carrion or a couple of Tomb Scorpions since these units can deither play the roll of distraction or charge the Ogres to stop them shooting whilst the rest closes.
As for my Plague Skaven I take advantage of the average LD values. Plagueclaws are your friend here as even a single wound causes a panic check on Ogres. Rack up enough of them and they will fall. Additionally as has been stated the spell Whither is a pain for Ogres. Then again Whither is the one spell hated by most players in my group since the permanent -1 toughness hurts a lot of opponents. Censer Bearers are also useful for getting close intothe Ogres thanks to being Skirmishers and they hit hard in combat as well.