uploading moderators maybe?
That would require hiring more staff to do non-programming work.
I mean really, there is a self-moderation aspect here, and that's to utilize an external service (eg members to my patreon/discord/twitch followers/subscribers,etc) and as long as you're signed into that service through the game, anyone you play with that is part of that discord server, will get access to those additional skins the discord server has already approved. Much in the same way discord and twitch have their own emoji stuff.
It's probably not super-trivial to do, but it would encourage those playing the same game on the same discord to use their custom skins.