Orks are entertaining and probably easily bribale. Plus they're latent psychics; if we can convince them that something should work, it will.
But fine, no orks, less dakka.
EDIT: any way to get us an Emprahsqueu? (I probably botched that spelling)
" This is due in part to how Imperial scholars now believe that they reproduce: Orks release fungal spores, which grow into a plant-like womb underground that nourishes the bodies of the various Orkoid species. This is the entire basis of the Orkoid ecosystem, producing first Squigs, then Snotlings who cultivate the Squigs and the fungus they feed on, then Gretchin to build the Greenskin settlements, and finally the Orks themselves. This means the Orks, wherever they go, will have an abundance of food, slaves and other resources, a moving Orkoid ecosystem that supports them as they unleash their WAAAGH!s
This also makes it extremely difficult to rid a planet of Orks, even if the initial invasion is defeated. Orks release spores throughout their lives, but release them massively at the moment of death. Without a nearby population of Orks, the alien fungus will eventually start the Orkoid life cycle anew. Decades after weathering an Ork WAAAGH!, settlements on a planet can find themselves faced with an unexpected attack from Feral Ork tribes coming out of the wilderness. The only way to effectively remove all of the Orks once they are on a planet is through a planetary Exterminatus action."
Gotten from the wiki. Orks are bad. Do not let them land.
Also, as far as the Emprahsque getting personally involved, probably not. He's busy finding Jaghatai Khan and the other Primarchs, messing with chaos, and some other things for the next few weeks.