When it comes to demons attacking humans? More than likely.
In-game occurrences aside, we see Nero do it in some of the cutscenes (such as just before the start of the second mission, out by the fountain).
I'm drawing a blank as to whether Dante ever did in any of the cutscenes, but off the top of my head, I can't think of any. He probably did, though...somewhere, at some point or other. :ninja:
Of course in Vergil's case, he stabbed his own brother...which I'm more than certain was meant to deliberately awaken his devil (though he probably enjoyed getting the upper hand on Dante in doing so).
But including gameplay, cutscenes, and so on, I'd say they probably are. It may seem like a dirty trick, attacking an enemy when they're down, but from a strategic standpoint (particularly Nero's and Dante's) it makes a lot of sense.
Logic aside, I think they also derive some enjoyment from it; Dante has conveyed it on a number of occasions, and even Nero seemed to get a sort of twisted amusement, depending on the enemy he faced.
In short, pragmatism plays a part, but I wouldn't say it's the only part.
(Sorry if I'm rambling; I've overtired, and on the tail end of a sinus infection, so I apologize if this makes little to no sense).