I always thought Warhammer lended itself more to epic orchestral stuff, like this with a little less percussion: View: https://www.youtube.com/watch?v=hvj2rLEWo7s
i think final liberation used metal well wasnt entirely metal but it was just enough to get you going
Should depend on your faction...heavy metal should be for chaos, orchestra for the SM, trance for eldar....orks...well what's that music called when you take household objects and bang them together repeatedly?
I imagine something with alot of drum beats would fit the orks, seeing as though they like to beat things to a bloody pulp. And just listen to the Ork theme in the original DoW to see what I mean.
As a chaos fan, NO heavy metal shouldn't be included. Imagine watching a live action 40k movie with excellent special effects. Throwing metal music into it, even for chaos, would be a horrible idea and be extremely cheesy.