In my experiences with the system from the court side.....everyone here gave you excellent insight. In my opinion, if you enjoy the company of your ex-MIL and it's mutual, then do what works for both of you.
Hydrogirl is very correct that passing a message to him is just as illegal as him passing a message to you. Just inform your MIL that the terms of the Protection Order means he cannot contact you by any means. This will most likely give your MIL a way to tell her son herself that she doesn't want to be a party to any illegal action. By that, I mean, you could have had him charged for violation of the PO and also violation of probation for using a third party to communicate with you and your MIL would have had to go to court to testify as much. I'm sure niether you nor your MIL wants that to happen.
In my professional opinion, almost all those with a Protection Order violate it just to test the victims resolve and to test the system. Even on probation, they will test the system. You are doing great by holding firm to your boundaries. Just keep in mind the PO works both ways and sometimes they will push you to the point of trying to charge you. Those jailhouse lawyers (cellmates) are a devious bunch.
You have the right to live in peace and that DVP and his probation rules give you recourse if that peace is infringed upon.