Were you having your payments auto-debited before you defaulted and got repossessed? If so, they've got your bank account numbers. Keep an eye on your account.
Also: When you signed the paperwork on the car (and I hope you still have copies of that paperwork,) they might've reserved the right to do that, in the fine print. Since I can't see your contract, I don't know exactly what you agreed to upon signing. Maybe they can come after you for it.
I want to say "No they can't," but the answer is probably in your copies of the paperwork. Unless you're filing bankruptcy, GMAC can come back to haunt you, be it through a judgment against you, or by whatever means are in the fine print of your contract.
Good luck.
After a vehicle is repossessed, the lender can get a judgment against you for the unpaid balance. The total is figured by taking the loan balance, adding the costs of repossession, storage, and sale, and subtracting the amount that the vehicle sells for at auction.
Once there is a judgment against you, they can ask the court to attach your wages, or to seize your bank account(s) to pay the judgment. If your name is on the account, even if it is not your account (such as a child on a parent's account in case of the parent's incapacity) the account can be seized!
The simple answer to your question is yes they can with a court order!
typically they cannot attach a bank account. However, they can put a garnishment on your wages if they send it through collections and are awarded a judgement.
