I don't think it would be rude at all.
Pups need to stay with their litter mates really until about 8 weeks I believe. They learn to socialise properly and learn the strength of their bite which they learn through play with their litter mates.
I'm sure the breeder would be OK with this. If not, ask why.
Don't be shy, pups cost alot of money and it's going to be with you a long time. It has to be right.
Bev