Dragonair is a oneWorld airline. It is a CX subsidiary, thus not listed separately. See:
https://www.oneworld.com/member-airlines/cathay-pacific (scroll down to the bottom).
Their lounge is fairly mediocre (at least for HKG standards) - use QF lounge instead (the same level, different entrance). Explain the situation and log to your account on smartphone and show them the status - should work...
There is no diffirence in access rules between Cathay Pacific and Cathay Dragon,although I agree the KA G16 lounge is not up to CX lounges standards.