I've read the books & hold a BA in classics, so now the name seems more unisex than before. Yet, I'd assume
Artemis was a girl, and if I'd use it, it'd be on a girl. I'd prefer
Artemisia for a girl or Artemas for a boy. (According to CKE, Artemas was a companion to Apostle
Paul.
http://www.behindthename.com/bb/arcview.php?id=704059&board=baby)