Greyhounds are trained to race using "prey", something that looks like a rabbit that's on a stick and raced around the track. They are conditioned to chase ... and kill what they catch.
The incident mentioned above happened across the bay. We had just gotten our pup, and I was shocked beyond words ... I hadn't thought of something like that. The man is 80 years old; he was walking his dogs. The greyhounds (all rescues) were inside the house. They saw the dogs as the man walked by and broke through the screen door to get out and at them. The man couldn't protect one of the yorkies, and the greyhounds tore it apart. A few teenagers sitting outside were trying to help, but all they could say was that it looked like lions tearing apart a lamb.
If you were talking about a greyhound that had never been trained, you may stand a chance, getting a puppy in with your puppy and being raised together. But to rescue a racing dog, a highly trained and motivated "prey" catcher ...
I'm sorry ... I don't think there's a snowball's chance in hell.
If your boyfriend wants a larger dog, get one as a puppy so they can be raised together. As it gets older/larger, it won't know that your pup is anything but a friend.