His PO has the power to put him in jail which is not the same thing as having the right to do so. The whole thing will get sorted out at your friend's VOP hearing. If your friend noticed he hadn't seen Fred the friendly probation officer in several months he should have called probation to find out what was going on. I guess now he knows.
I agree with Mr. Kaman, that the PO has the ability to file a VOP, whch can result in incarceration. I suggest that since your friend is incarcerated for a VOP, that they need the assistance of a lawyer. Most VOP are based upon a failure to comply with the standard conditions of probation, which include reporting as required. Therein seems to be the issue in this case, as to where and when the reporting was to occur. Get the lawyer. Get the advice. Good luck.
This response does not constitute legal advice. Given the nature of this website, it does not create an attorney-client relationship. This answer is provided solely for informational purposes, for you to use as a starting point when speaking directly with a lawyer in your State. I urge you to immediately contact an experienced criminal defense lawyer admitted to practice law in your State before you make any decisions about this case.
Yes, the probation officer can arrest a probationer where probable cause exits to believe that a violation of probation has occurred. Felony probation violations typically result in a no bail hold on a defendant until he or she is produced in court for a hearing as to whether probation has been violated. The probationer can request bail at this hearing, or a release on his or her own recognizance.