Yes. If it's literally read-only then it's safe and easy (just use read-only nullfs); if it's to be writable, but read-only below (like overlayfs), you'll have

Yes. If it's literally read-only then it's safe and easy (just use read-only nullfs); if it's to be writable, but read-only below (like overlayfs), you'll have to use unionfs which is still a bit... temperamental.