This isn't exactly a new tactic, and isn't exclusive to the Ogre Kingdoms army. However, it can work and Gnoblars do indeed block line of sight to Ogres (however silly that seems

).
The big downside of this tactic however is Gnoblar Bickering. If your Gnoblars screening your Ogres suddenly start Bickering on you, your Ogres will be stuck behind them instead of continuing the march forwards. Also, Gnoblars move more slowly than Ogres (4" compared to 6"), so your Ogres will not cover as much ground per turn as they normally would without Gnoblar screens.
I personally wouldn't use this tactic much, perhaps with only a select element of my army if I desperately want one of my units/characters to avoid being shot at.
By all means give it a go and see how it works out for you

If you want to put your Gnoblars to good use, I suggest using them as a support unit for your Ogre units. Their ranks and number can really help swing combats in your favour at key moments in the game.
Also, at 40pts for the basic unit, Gnoblars are superb at taking and denying table quarters.
A table quarter is worth 100pts, 60pts more than the unit of Gnoblars that holds it
