The short answer is - yes, you have a better chance of getting a healthier yorkie from a breeder that tests her breeding stock and has good lines behind their pedigrees.
Still yet, a good pedigree doesn't always mean a healthier dog. I do remember at one point there was speculation that a very popular show dog stud was responsible for bringing liver shunt into several lines. This dog appears in many yorkie pedigrees I've seen.
__________________  ~Ruby, Reno, Razz, & Jack~ |