New customers only.
BUT it's pretty easy to get a hit as they don't ask for your address if you do streaming-only. So use a different e-mail address and credit card than the one you used before. Netflix then has no way of knowing you're not a new customer.
(Ethically I wouldn't feel bad about it in this case, since if it's been several years you really kind of are a new customer)
Don't forget though, that you have to keep the subscription at least six months. And it looks like that may be enforced this year. If you cancel before six months, ALL of your GS miles will be forfeit, even ones earned on other hits.