Replacing the owl in the nest can entail some athletics if the nest is high, and some risk if the parent owls are of a large species and misinterpret the generous nature of the climb to the nest. But when possible, successful replacement is the most effective course of action from every standpoint if you find an owl on the ground.
It is becoming common place for many rehaber's to place orphaned owls in other owls nest where a family of owls are brooding owlets. The parents will except the owlets as another mouth to feed and as rehabers will tell you it gives the owlet a chance at a free life in the wild. What is better then that ?