My dog has a cracked tooth. Should I be concerned and see a vet?

Hi there. This is a very good question.
Based on the photo, this type of tooth fracture is usually referred to as a "slab fracture". Dogs often get these from chewing on hard objects like bones or rocks.
Although I can't see too well on the picture, I would be concerned about the pulp cavity being exposed. This is the area that runs throughout the length of the tooth carrying blood supply and nutrients to the tooth. If exposed, there is a greater likelihood that the tooth can become infected and decay quite rapidly. It can also cause pain in the mouth.
Freddie's veterinarian can check with a dental probe to see if the pulp cavity is exposed. Sometimes this can be done while the dog is awake, but sometimes it has to be done under sedation or anesthesia. If Freddie has a bit of tartar, you can just schedule a teeth cleaning and his vet can check it out then. If the pulp cavity is exposed, extracting the tooth is recommended to avoid infection and pain. Once Freddie's tooth is removed, he probably won't miss it. A soften diet and no chew toys for a couple of weeks and he'd be good to go.
I hope you find this answer helpful. Best of luck!