Hey Taz,
I, too, think it's wonderful that you're willing to help addicts in need. 2ala2 gave you the same suggestions I was thinking.
If you're only going to NA meetings as a visitor and to observe, I doubt if you'll have a need to introduce yourself. Whether the meeting is open or closed, non-addicts aren't supposed to participate verbally. Yet, you say you understand that alcohol is a drug, so you shouldn't have a problem with referring to yourself as an addict. When sharing, just be mindful to avoid drug specific language and sharing on the spiritual principles of the steps is something you can never go wrong with.
From what I understand, when NA was new, most addicts had AA sponsors. My sponsor has over 20 years clean and told me his 1st sponsor was an AA member. Good luck and enjoy!