He only way to really know if a horse has ulcers is to get them scoped. The vet can do a fecal blood test and get a pretty good indication, but this is not 100% accurate when it comes to diagnosing ulcers. I have never heard of the running the cap over them thing? One of the biggest indications of ulcers is losing weight. It sounds like your horse has been doing a great job of gaining weight, so you may not have to worry about ulcers at all. That topline is very hard to fill! It is more about gaining the muscle back there, not so much just gaining weight.