Multiple times Urban has dismissed a player and let him back on the team after the situation is 100% known. Sprinkle, Klein, Hyde (suspended indefinitely), etc.
Sprinkle's situation was announced as a suspension, pending the outcome of his legal situation, not a dismissal.
Klein was dismissed, but in the statement announcing his dismissal, the door was left open to re-evaluate his status if there was a change in the charges.
Hyde, as you noted was a suspension, not a dismissal.
I'm not saying Dunn won't return, but his was a announced as a dismissal, with not mention of an opportunity to return, as in Klein's case, FWIW.