No, don't tip a hotel manager. In many properties they aren't even allowed to accept tips.

I worked my way through college as a hotel bellman; if a manager had to help out in a traditional tip collecting capacity, ie., retreiving valet parked cars, delivering bags to guests' room, etc., he/she would distribute any tips received, evenly among the tipped staff on duty at that time.

+1 on writing a letter (or even a hotel comment card) praising the manager on his service. I worked at two Hyatts, and a very busy Marriott in Boston, and I assure you comment cards make their way back to employees who are mentioned in them.