It's against the rules of the contest since it was clearly stated the you need to submit your own art as entry for the contest but it's still up to you on how you will handle guilt since there is no way to determine if your entry is commission or not if it's done outside the forum but the stated it was forbidden.

There is a reason I have "up to 2 artworks" in the contests as of late, as I had a few regulars reaching out asking if their parent or significant other could submit something so this way you don't have to do any of the shady shit but can just post their work from your account and if you win you send them the prize.