Sure, this arrangement is commonly called "stealth master". For example, see the article Why you should use stealth master DNSWhy you should use stealth master DNS.
The DNS system does not make a distinction between "primary" and "secondary" DNS servers. There are simply a bunch of NS records listed for each domain, their order or priority is not relevant (they are all presumed to contain the same data). How you arrange distributing the data amongst those NS servers is up to you.