Breeding half-siblings is inbreeding (or an extremely close line-breeding, depending on your definition). That is something that should only ever be attempted by people who are very familiar with the line (family) of dogs they're breeding and who have intimate knowledge of any recessive genes, traits or defects the dogs are carrying. It's the sort of thing someone might do if they'd been breeding that particular line for six or seven generations. It would be highly irresponsible to jump into a breeding like that without that in-depth knowledge and experience of that particular line within the breed.
I presume these dogs have been screened already for hip dysplasia and cardiomyopathy, and had their eyes and thyroid panels done. If not, they shouldn't be bred at all. And this is exactly the sort of breeding that is the *most* likely to produce affected puppies if the parents have not been properly screened for genetic defects. Because with breeding such close relatives, you're far more likely to have hitherto hidden or unexpressed genes doubled up and defects exposed.
