Do you have a copy of the contract you signed with the CU? We have a similar issue - one of our vehicles is financed with a CU, we each had a credit card and I had an unsecured loan. I pulled the docs on the vehicle, and the cross-collaterization piece is buried in the fine print.
As an FYI, our attorney advised us to let the vehicle go. He said that CU's are notorious for adding the balances on CC's and unsecured loans to the balance on the vehicle. In our case, that puts us very deep into negative equity land on this particular car. We were current on everything until the day we filed on July 5. So far, they haven't contacted the attorney about us surrendering the vehicle, so we are keeping it insured and driving it until they come get it or we are told to drop it off somewhere.