Before, after, and on the beat are all viable techniques I subscribe to, and use, but the drummer need not. Playing expressively to a rigid track is not a stretch. I think having a constant beat is so much better than fluctuating to accommodate skill level, or volume changes. All the expression can come from the other instruments.
As a soloist (horn player/singer) I often take liberties with the feel while my track, or band members stay solid. Since they were invented, I always said that ALL drummers need to own, and play with a drum machine. It makes them better drummers.
Just my take on it.