There's no obligation for any player to stick to their own lane in professional play. If, for example, a team thought they would have an advantage by putting an ADC mid and swapping the mid laner down bot, they would absolutely do so. Or if they had a flex-pick in the top lane, who picks smite to go jungle while the "jungler" (without smite) covers top, they could do so. There are no rules preventing that.
However, teams rarely, if ever see an advantage doing so. This mainly comes down to practice. Most professional players don't have the time to practice outside their role. They don't know the matchups and intricacies of the lane/jungle pathing. Even players that regularly practice other roles, or used to play other roles get completely smashed when playing an off-role (Piglet in mid, Aphro on ADC, and Alex Ich in the jungle)