hey, i know those! i translated those at one point, and they're all really cute! however, yeah, i'm pretty sure you're right, you'd have to get permission from that artist specifically, i think. they made those stickers as a submission for a contest (which contest, i'm not entirely sure? it sounds like JPN elsword team, or JPN line themselves?? might've held one for this or something, but i don't know the details) and won. however, they still don't know if the stickers are actually going to be sold or not. (last time i checked at least, maybe i can dig around and find out)
so, they're still the property of that specific artist and no one else, and you'd need their permission to use them, basically. which i'm not sure void would be able to get, considering it's just one person who made them and void is a big (overseas too!) community. ^^;
i think the rest of the emojis on the NA forum aren't here for a similar reason, since they appear to have been made by community members specifically for NA forums.