Depends on what each person actually believes. If a Creationist and a Darwinist are arguing about evlution, but the Creationist argues it's evidence of natural selection, whilst the Darwinist argues that it's just part of God's grad design, are they both being devils advocate?

More commonly, woud be two people who are in rough agreement, each illustrating the fact by being 'Devil's Advocate-ier than thou'. Especially so if they're talking about abstracty esoteric stuff, 'cos with such subjects, it's often as easy to define a thing by describing what it is not, because you're not exactly sure what it is in the first place.

I think I need to go look at some cup marks...