I don't know if this rule is good because anyone can commission an art then submit it here so its unfair to the real artist who work with his craft to make things done according to this contest. But its part of their rules and actually its hard to spot if the submissions belong to the real artist since anyone can claim that he create that art. Anyways still good to see some good arts keep posted and I enjoy browsing to see new submissions.
It's all about honesty and conscience then. I don't remember the exact name of the contest (PS: I remember it now, it was the Christmas holidays) but I think it was in 2020 when I asked Hhampuz if I can join the art contest made by my cousin, and he confirmed that it is possible, I think it is still allowed.
What I did is I opened this to my cousin, I've been transparent to him, I gave him the links especially the contest thread so he knows the rules and the prizes. I can say that I've been fair to him. I also told him that he will get the full prize if he ever wins that day. But even he didn't win, I still gave him money for doing it for me, a compensation for his talent, I gave it to him when he celebrated his birthday, Valentine's day.
It is allowed to submit an artwork created by your relatives as long as its original and not plagiarized. But I agree its in our conscience if we will submit a commission art and then keep it secret to the real artist, because if you're honest you'll let them know what its all about. On the other side, its a bit risky to ask someone to create an artwork for you. Come to think of it, you'll pay him/her for the the artwork so you can have an entry, but there's no guarantee if that artwork will be chosen as a winner right? In the part of of an artist, win or lose he/she is already paid even he/she is not aware of how you're going to use the art you asked him/her to do.