Are you sure ACR is actually reading the WB data and not just guessing? My understanding was that they would just guess at the WB -- I believe based on the plain text description for in-camera WB setting, which is not "encrypted". If in-camera setting is Auto or Custom, it will just attempt to guess the WB based on its own Auto WB method.
I guess someone could test it. Set a really weird WB and convert it via ZCR 3.1 and see if it keeps it weird or makes the photo look right. I'm thinking maybe set a custom WB off a yellow piece of paper, then photograph the yellow paper in a normal scene and see if it comes out yellow or white.