In most cases involving a criminal probation, you are normally ordered not to pick up any new "criminal" offenses while on probation. A seat belt violation is considered a civil traffic infraction, not criminal. Be mindful that I have heard judges order a probationer not to even get a traffic ticket while on probation, but I have yet to see a Judge actually violate a person's probation due to a civil traffic ticket, unless that persons drivers license was suspended and the person was not supposed to be driving in the first place.