Currently the incidence of elbow dysplasia in the Boxer breed is 0% - there's really no reason for it to be part of the ABC recommendations. Breeders/owners who are involved in Agility or Utility might want to have elbow x-rays done, because those sports are high-impact for the elbows, but with a 0% affected rate it is not what I would call an important screening....
CERF, as well, is optional at this point; the primary eye issues with Boxers are entropion/ectropion and distichiasis, which you actually generally can tell the dog has by looking (and by the irritation of the eye). While these conditions may be hereditary (or may be due to the conformation of the Boxer head, which would make it hereditary in a different sort of way), they are not widespread at this point, and generally do not affect vision, health or longevity unless severe cases are left untreated. Certainly if there is a history of these problems in the line, CERF testing is a good 'safeguard', but again it is not what I'd consider vital.
If this breeder does hips, thyroid, and the two heart tests (for AS and ARVC), then you're ahead of the game.
