My vet sells greenies at his office. I sent him a letter that I copied from here about how terrible greenies are, and the next time I saw him, he thanked me. He said that he will, however, continue to sell greenies, as they are decent dental help for dogs who do not get their teeth brushed by their owners. My letter did make him have a training session with his staff, and they were all instructed to council anyone who buys them on the possible dangers, and to make sure they monitor their dogs while chewing.
My vet said in his 15 years of experience, he has removed multiple things from dog guts, but never greenies.