I think the breeder only worries that the puppy may get an upset stomach. Most puppies do okay with boiled chicken breast, as it's easy to digest.
If you want to give treats for training, I'd start with very little. A dog meet organizer once made fun of me for giving my babies "lint-sized pieces" of treats. Said she couldn't even see it!
But, it's because I know my babies have sensitive stomachs.
But...I'd say hold off on the treats until the puppy has settled in and starts to eat regular meals first. Last thing you want is a puppy who refuses kibble and demands only treats.
