[@Sarpedon]
Actually, I'm not so sure. Tyranids don't feel rage (do they? I'm not sure but I imagine that the Hivemind doesn't and the individual Nids aren't smart enough for that) and Ork conflict fuels Gork and Mork (or should the be Mork and Gork?) so I think Khorne would just have to sit and watch. To be fair, I imagine a lot of daemon breakthroughs would end up happening so some of his followers could probably join in.

[@BCTheEntity]
I vaguely recall that but I've read a [i]lot[/i] of Ork fluff, both official and fan made, so I might be misremembering or confusing fanfics with official releases.