I agree with shelleyb that IF it's true the hatchery has those lines, their stock might be good at first. However, it would not take very many generations of having them all mixed in, thrown in the same pen, before they'd begin to pull bad traits.
I also hatched some yellow legged chicks from a well known breeder who was getting top $ for her eggs at the time - the pics advertised looked to be very nice stock. What I ended up with was not. You have to do your research, and I should have asked for more pictures and asked more questions. I typically do ask a breeder what they are working on in their breed pen at the time I order eggs...that also tells me where they are in their breeding program. But, I didn't ask a lot of questions this time (it was a BYC-er and I just assumed her flock was established, but come to find out, she was just starting out). I got: yellow legs in one, a few solid blacks, a few super mossy, one with terribly bad fused toes, and one VERY nice keeper.