There is always an increased risk of incarceration whenever a person has a new offense which also violates his or her probation. There is not enough information about the cases and his entire criminal history to determine the possible results. However, I seriously recommend that you retain counsel for him. For both cases. We handle Riverside cases. www.taubcriminaldefense.com
The information provided herein does not create an attorney-client relationship. The information provided is to suggerst some general principles and should not be relied upon for client decisions. Only upon the hiring of counsel can such advice be custom-tailored to the client's specific situation and needs.
If the arrest was after he got probation then it would not be a violation. If afterwards, it could be depending on the facts. See my answer to your related question about Prop 36 probation grants in general.