Yes, these are independent. Though, to be a grotto officer you must have both. It is recommended for everyone to do both. With an NSS membership you get:
1. Your own unique NSS id.
2. Access to the NSS membership directory.
3. A discount at the NSS bookstore.
4. A subscription to the NSS News.
5. Access to old NSS convention guidebooks.
6. Access to American Caving Accidents.
7. A discounted fee for attending the annual NSS convention.
8. Ability to register for the TAG Fall Cave-In without having to be someone's guest.
9. Eligibility to vote for the NSS Board of Governors
https://caves.org/committee/membership/index.shtml