I havent come accross any guidlelines as such no, but it might be worth having a look at our hamster club websites they list show standards for this country, I assume that would include weights, but as I dont show myself I have no idea.
Here is a link to the NHC show standards -
NHC Exhibition Standards - Dwarf (Any Other Species) - National Hamster Council
I had a quick look and it didnt list any figures for weights, just minus 5 points for excess fat, but dwarfs are natually round and chubby anyway. Also hamsters dont over eat, they will only eat what they need, so unless they are being fed extremley fatty foods and a poor diet I dont see how they would get too fat, unless of course they was some underlying health issues.