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.
Haha, it's not practical to hire and pay artist to make a roobet entry. What if the participant didn't win? He's just fooling himself at the same time it won't give him a guarantee to win

well, nothing is guaranteed and the contests have lots of good entries but not many of it are done at a professional level so may be worth the shot
I don't think it's pure waste
I like the idea of thinking in bets.
just to make it clear I see no big problem on commissioning someone to participate unless it's clearly against the rules