DC owns the rights to Chloe as a character. They should be able to do whatever they want with the character.
I'm not sure that's the case. Just because a character appears on SMALLVILLE doesn't necessarily mean DC owns him or her. It all depends on the contracts involved, Warner's current contract with the screenwriters' union, etc. I don't know for certain that this is the case, but it's entirely possible that that the screenwriter who created Chloe would have to be compensated for any comic book appearances.
In which case, there might be significant legal hurdles involved.