What is the hole in this turkey?
I'm intrigued by this question, so I'm posting an attempt at answering it, hoping it would attract a better answer by an expert.

I am not a vet, but to me it looks like an injury that didn't have time to fully heal. Since the mass production of poultry emphasizes fast growth of the birds, it's not that surprising to me.

These birds are often kept in a sub-optimal environment, so the injury could have been infected too, but it did not become bad enough for the turkey to die from or for the producer to deem the bird worthy of discarding or butchering into smaller pieces.

Was it safe to eat? Probably yes. The quality of the meat may have suffered to some degree though.