You know, I never pressed for an answer, but the impression I got was that they didn't see it as necessary. The ones I have gotten to know a little or know a little about, all have been doing this for so long, and have been breeding their own lines or only co-breeding with certain other breeders that they seem to know who has what problems.
I know Jack tries to minimize the risk of heart problems by using studs who are a bit older, also. (Cardiomyopathy -forgive my spelling- usually shows up around age 4 - 5, I think.)
This is part of why I think it's good to ask other breeders about a kennel you're interested in. The breeders watch each other's dogs at shows and pay attention to whose having what troubles. When Heidi's breeding was being set up, I was asked a set of questions about her past health history by the owner of the stud (Cardale Boxers). No specific testing was done though, because she knows Jack's dogs, she knows the health history of his line by virtue of just knowing the dogs, and she's known my dog since she was a little pup.