Greg Weisman, One of the producers was asked a question about the team diversity of races and he answered saying: 
  Artemis is also a minority, she's half-Caucasian, half-Vietnamese.    
Finding out this info was a awesome find I love seeing that cartoons are getting more diverse such as Teen Titans was very diverse with different race of characters. But the question still remains who is Artemis, he says she's an existing characters in the DCU? Who do you guys and girls think she is? Cartoon Network already revealed she's Green Arrow's Neice. Then now we have this new information below. But could Artemis be the female version of Conner Hawke, since this is a different Earth, is it possible? Now that I think about it, on wikipedia Conner Hawk ethnicity is stated:  
Connor is of mixed Asian, African, and European heritage (his mother was half Black and half Korean, and his father Ollie is white), and was originally depicted with Asiatic features, dark skin, and fair hair and eyes. However, this has not been consistently maintained across different artists and colorists, and when the Green Arrow series was rebooted the character was depicted with European features and light skin (even though a childhood picture in the later Archer's Quest storyline depicted him with dark skin). Connor's original features were later restored with Dixon's Dragon Blood miniseries. He now appears to have a mix of Asian American and African facial features.  
 
Then you add that Artemis is also a minority, she's half-Caucasian, and half-Vietnamese.       
   http://www.s8.org/gargoyles/askgreg/search.php?qid=12838    

Artemis was in issues 24 and 25 of YJ. She was a member of Zandia's olypmic archery team. She and Merlyn were competing against Arrowette. She fought Impulse and said she wanted a different opponent after Bart caught all her arrows. She is Huntress' daughter. When Arrowette's mom saw Huntres aim a crossbow disguised as an umbrella at Arrowette, she threw her lighter on Hunters making her miss and hit Merlyn in the arm instead. Artemis was disqualified, Merlyn unable to compete, and Cissie took the gold medal.     
 

She could be an alternate version of Rose Wilson.
 
The character designed for the Justice League in Young Justice are lifted directly from Crisis on Two Earths.  Towards the end of that movie, Martian Manhunter wonders if there is an equivalent of Rose in his own universe and promptly realizes that she'd be an evil counterpart.  In that universe, Slade Wilson stayed with his first wife and had a red-haired daughter.  In the Young Justice universe, perhaps he had a daughter with Lillian Worth instead?

Artemis' character just got more interesting and less disposable... great info and theories :)

"My belief is that she's Tigress, the Sportsmasters daughter. After he appeared in Drp Zone, I'm suspecting she'll be "The Lights" plant on the team.  Just my theory "

I'm almost positive she Artemis Crock if you watched episode 6 it will almost prove it.

i have a few guesses as to who Artemis could be. And I have a particular #1 theory of who she is.
 
 We know however that she is NOT WONDER-GIRL OR ARROWETTE, since greg weisman has said that she is not. Hopefully people will read that and stop posting that idea. . 
 
THEORIES & REASONINGS 
(taking into consideration that these characters would have been revamped for the show, either in tweaks biographically or in how they look)

Sin - Her origin works with what we know so far in the show, she is the adopted daughter of Green Arrow and Black Canary in the comics. They may have just made her Green Arrow's made-up "niece" for the show. She was chosen, and trained to be the next Lady Shiva, which could be how Cheshire knows her. And how the league of shadows/ assassins know her
 
Cassandra Cain - She was the biological daughter of Lady Shiva, and was trained to be an assassin in the comics so this would fit with how Cheshire would know her. She also is connected to Ra's Al Ghul somehow, who is supposed to be in some upcoming episodes, im sure theyll use him to further the traitor storyline. 
 
Stephanie Brown - im only saying Stephanie Brown because i think they may be using her name with Cassandra Cain's bio/ origin, and maybe they are looking to use the Spoiler persona.
 
MY BEST GUESS AS TO WHO ARTEMIS IS...
Ravager - as Deathstroke's daughter she originally was a traitor of the teen titans. Impulse develops a crush on her, which would coincide with the Artemis/Kid Flash love angle they are hinting at. Being Deathstroke's daughter would be the connection to her and the League of Assassins/Shadows and Cheshire.  I also think that with her there it would be a good way to bring new stories and villains like Deathstroke and Ra's Al Ghul.

I wish for more info