Yes. In fact you can use them now to extend your existing subscriptions.
Go to http://billing.microsoft.com and sign in with your subscription LiveID. (Open OneCare and click help/about to view the subscription LiveID)
Select the OneCare subscription and click on the renew link.
Choose the option to renew with a prepaid PIN or token which is the retail product key.
Enter the 25 character key and proceed.
-steve