If they did make an obvious ripoff, the moderators/artist should be able to call them out for plagiarism. The same should apply on any forum where an artist is claiming the work as their own, and the design is not to be used for commercial use to any extent. But I like to believe that Game Freak is wary of their artistic fanbase. If they ever did make a Pokémon based on any fanmade -mon, it would be a design that the artist has willingly given up the personal and commercial rights to use for themselves, since every official Pokémon and character is licensed by Nintendo.
OOOOR the artist could just ask Nintendo why they did this and if they could provide the artist credit for the artwork.