Hi there,
you can definitely be referred no matter if you are an Emeralds member or not. But as far as my knowledge goes, the Emeralds membership should guarantee an interview invite. So you should really look at how you play your cards.
I would recommend you to reach out to the BCG HR of the office you're applying to clarify any questions regarding the application (this is not impacting your application chances at all).
Hope this helps!
Cheers
Jonas