Is your character a magic user/otherwise magical in some way?: Yes.
If yes, can Artemis "sense" this?: Yes.
If yes, is there any specific impression that he would get from them?: Mostly alteration magic, with a dash of darkness/shadowy crap.
Anything else?: She's also a changeling! Only in this case, the human who got kidnapped, not the faerie left in the mortal world. I have no idea if he'd be able to sense that or not, but there ya have it.