If the address listed for the alternate payee (AP) is "c/o J. Doe" and AP is not J. Doe, does this belie the requirement that the QDRO list the AP's address?

Probably more significantly, does the plan need AP to sign a written authorization for the plan to send any information about the QDRO or awarded benefits to "J. Doe" as a representative of AP before the plan can use that address?

I'd say it becomes a fiduciary issue: i.e., is the fiduciary on notice that something may be rotten in Denmark, and therefore must perform some kind of due diligence? I'd say Yes, even though you have a court order/QDRO, because the QDRO is confirming the parties' agreement and trying to meet ERISA QDRO requirements, and is not necessarily confirming that the checks are being directed to the proper person at the proper address. Perhaps the fiduciary should start by rejecting the QDRO due to the c/o. (For example, I've seen a QDRO rejected, rightly or wrongly, because it directed that payment of a portion of the participant's benefit go to the lawyer and the QDRO was not signed by the participant.)

The down side is a potential claim against the Plan (although the Plan was just following the Court Order and some bank will have cashed/processed a check with an improper endorsement); the upside is getting it right.