I can’t speak to the rules of an Evermotion contest/challenge; you’ll need to go to them for specifics about their rules.
As far as Epic is concerned, you are free to use Learning tab assets for something like that. Some of these assets are designated as UE4-Only, in which case they can only be used in UE4 (rather than another game engine). So long as you’re not using another engine, it’s fine.