Mako was the only person of an Asian ethnicity who did voice acting for the series...
That's untrue. Dante Basco (Zuko) is Filipino-American. Other ethnically Asian cast members in recurring or guest roles include Jennie Kwan (Suki), Sab Shimono (Monk Gyatso/Master Yu), Takayo Fischer (Lo and Li), George Takei, James Sie, Brian George, Clyde Kusatsu, Keone Young, Lauren Tom, Brian Tochi, Kim Mai Guest, James Hong, Tsai Chin, Derek Basco (Dante's brother), George Cheung, and Karen Maruyama.
The character in the cartoon does not look Tibetan or Chinese. For reference, here is Aang:
Here are some Tibetan children.
In animation, large round eyes are a signifier of youth. Look at the child versions of Zuko and Azula in flashbacks, and they have the same kind of large round eyes. Within the graphical language of the animation design style being used, yes, Aang looked just as Asian as every other child character in the series. (For one thing, that image you're using isn't accurately colored. Aang's complexion isn't so pink: http://images.absoluteanime.com/avat...ang%5B2%5D.jpg