I think you're probably right about it being an azeala. Might be why it looked so familiar, since I have azeala plants in front of my house. I know not all hibiscus are large, but it just doesn't look like a common hibiscus. Not to mention that the hibiscus isn't at all common in New Jersey.
Went on a Flickr photostroll to the NJ Botanical Garden over the weekend. The highlight was the social gathering, but I came away with some decent shots.