Hiya,
at a lot of the shows the pet class is judged by someone who is 'hanging around' looking like they have nothing to do! lol - obviously they are usually someone who is known to the show sec and who are known to have experience with hamsters, but that is all they need really as the pets are judged on condition, tameness and the enrichment in their travel cages etc.
Sometimes show judges are used too if they happen to be at the show with no official job to do.
So as you can see each show usually has a different person to judge pets so they probably wouldn't recognise the same hamster anyway, but there isnt a limit to how many times you can enter your hamster in to the pet class - it is completely up to you
Tammy x