Yup. We have no enforcement of where the Subscription ID is used right now. We do log requests to check for abuse of IDs so that we can change them if we determine the ID has been distributed publicly. Beyond that though, if you're using a Subscription ID for websites you own, per our Subscription FAQ, you're free to use the same one on all of them.
www.sourcecoast.com/extensions/subscription-faq
Hope that helps,
Alex