Probation Officers are treated differently in many states in regards to "police powers." But warrants would be preferred and police with legal standing should do the arresting. However, I believe probation officers have the powers to search for illegal activity without warrants as stipulated in the granting of probation. That said, if all criminals served their full sentence, there would be no need for probation and any applied costs. In my city, criminals use probation as a swinging door back into crime.