Yep! You can enter each contest once, so long as you have a different entry for both. So if you’ve got more than one idea, you’re more than welcome to submit them both, so long as one goes through deviantart and the other goes through fanfiction/AO3/tumblr. The entries must be different for each contest 🙂
Information on the deviantart contest here and for the tumblr contest here.
Brothers Apart 