Counterpoint isn't the same as polyrhythm, but counterpoint can be polyrhythmic. Counterpoint is a second melody that runs parallel to the main melody, while having an independent melodic voice of its own. Listen to Bach, and you're probably listening to counterpoint.
As for polyrhythm, the approach I tend to take is that if it happens naturally, I'll spend the time learning how to play it. But I don't consciously use these devices.