Dude,
Sorry about the above post. I gotta learn to read something THOROUGHLY before replying.

If they tried to serve a warrant for your nephew at her (grandma) address, and she told them where he could be found and they didn't bother to look for him, then you are in pretty good shape. The State HAS to show that they made a diligent effort to locate him. And that diligent effort has to be more than a "cursory records search" or a stop at his last known address. An attorney can extricate him from this most likely.
Now if those papers were a summons, or other legal papers not related to a warrant, then worst case scenario is he gets a failure to appear warrant. That sux also. because he will already have established a propensity not to show up for court and it is up to the Judge if bond will be allowed. Someone with a history of failure to appear can expect a rediculously high bond, IF they even get a bond.

If he's going to court on a case in which he has ALREADY been convicted (or adjudication withheld) he cannot be re-tried. He CAN be brought back for sentencing in the event of a withheld adjudication.

Sound like his PO dropped the ball. People on probation move. It happens daily. It's up to the probation officer to ensure that you are fully aware of the process, and paperwork necessary to effect a transfer as long as the transfer was in state. It then becomes incumbent on your nephew, or his guardian, to follow thru with it. If he drops the ball.....

You need an attorney. Do NOT go into court in this case without one.

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You can lead a Horticulture....But you can't make her think!!!!