In my experience, copperheads are aggression. I've only experienced the cucumber smell once, and it was in an area know for copperheads.It makes sense to assume it's true, as there's no downside to believing it. Smell cucumber where it doesn't belong, assume there's a snake, and react defensively.
On the plus side, copperhead bites are very rarely fatal, and they often do not inject venom when they bite. On the down side, one source said copperheads account for the largest percentage of snake bites.