I've participated in three fairs by now, always with a different sim per contest. There's four sims in the household, but I submit just one entry per contest to keep it fair. So one sim submits entry to one contest, another to the second contest and two others take a break for that fair.
First fair was cow + milk contest. Cow got third place ribbon, no mention of the milk whatsoever, no info, no participation ribbon, no winner declared for milk.
Second fair was oversized crop + pie. Both entries won the first place.
Third fair was llama + wool. Llama won the first prize, but wool was not mentioned at all, no participation ribbon, no text or announcement of any sort.
I always sell and shop at the kiosks and do talk to people while there, although actually I did stay most of the crop + pie fair in the pub playing don't wake the llama. However, during the winning time on third fair they were all playing llama as well, although had been doing errands earlier. No idea if it's related or not.
In my game what I have noticed up til now is, that if I have one sim enter two competitions, one entry will get ignored, if I have two different sims participate (for example one enters the egg competition, the other the chicken competition), they will both receive rewards.
