They may be shown (and should be) but cannot get BOB and APA recognition if they're large fowl. I have shown them several times in the past. As for the bantams, SC barred leghorns are recognized both by ABA and APA (I was instrumental in having them recognized at a show in WA state in the early 1990s). In order to make sure we would have enough birds I put up every bird (except 2) I had but brought home a bad disease and lost every one of them. It was quite devastating because I had put in many years of breeding to get to that point, and I subsequently lost touch with some of the other exhibitors (Mr. Hickman in Oregon passed away shortly thereafter). I have since redone the breeding program and finally this year have a pullet that shows a lot of promise, actually better than anything I had before. I believe I'll be able to breed some more of the same quality in the coming year.
Raccoons, dogs, and owls have made a major inroad in my large fowl barred, and I have only a single (old) hen left. A mating with a SC black leghorn did not produce the desired result, but I'll try again in the hope that she will still lay a few eggs this year.