Answer: Praise be to Allaah.
What I think is that there is nothing wrong with that, because the Prophet (صلى الله علیه وسلم) listened to the recitation of Aboo Moosaa al-Ash’aree (رضي الله عنه) and liked it, and said to him,
“You have been given a beautiful voice like that of Daawood.” He [Abu Moosaa] asked, “Were you listening to that, O Messenger of Allaah?” He said, “Yes.” He said, “If I had known that you were listening I would have tried to make it more beautiful for you.” [Muslim, Salaatul-Musaafireen, 793]
So if this Imaam has a beautiful voice and recites well, and that will motivate these students, then there is nothing wrong with that, especially since the regular Imaam has given permission for that. The regular Imaam is to be thanked for giving his permission as that serves an interest.