This study involved different punishments for drug/alcohol violations at a college campus. It compared the effectiveness of motivational discussions vs. a $300 fine for a violation. Both were pretty effective in the short term (4 months). But a little more surprisingly, the discussions were more effective in the longer term (15 months).
Frankly I'm surprised the little interventions worked that well. I would think the short-term effects would happen because it's embarrassing, but I find it hard to believe they're convincing. All the alcohol education seminars I heard about in college were kind of a joke.
Of course, this would depend on the type of violation we're talking about. A violation where other people are put at risk (hazing at frats, drunk driving) is something that somebody can be guilted into not doing again. Offenses for loud parties or possession, where the most the motivators can argue for is the hallmate's study habits or the offender's own health, are a little harder to use guilt against.
Now, if part of this "motivational discussion" included them saying to the offender "Next time we're turning you over to the cops", I would understand.