If a lot of ground beef is fed, I would worry about the lack of bone in the meat. It seems to me that it could throw off the phosphorous /calcium ration, if fed over a long period of time. For instance, this could be unrelated, but I had a amstaff that I fed regular kibble and then added about 1/4 pound of ground beef to his food. I did this for many months. The dog ended up with Panosteitis. This condition, is usually unheard of in pits and amstaff(usually very large boned dogs and herders). I feel it was the ground meat without bone. The dog recovered fully and never passed it on to his off-spring, but I was worried for awhile.
For this reason, I would stick with meat with bones, or supplement with bonemeal with the burger.