Should the Imam ask someone who has led people in prayer without his permission to repeat his prayer?

The regular Imam has priority in leading the prayer. With his presence or his habitual delay, it is not permissible for anyone else to lead the people in prayer except with his permission. Whoever leads the prayer without his permission has committed a forbidden act, but his prayer is valid. The sin occurs by overstepping his authority, and the prohibition does not revert to the prayer itself.