From the webpage, I gather that this is a method of detecting hind-gut ulcers, which you can’t really scope for. This method detects blood in the feces.
The usual method for detecting stomach ulcers is to scope. From this webpage, I am unclear if this fecal test is also claiming to diagnose stomach ulcers. It does say that it helps distinguish between foregut and hindgut issues, which is not quite the same thing. My question would be, would the blood and protein shed by stomach ulcers make it through in measurable quantities to the feces, or would the blood and protein be digested in the small intestine?
The hindgut/large intestine doesn’t digest protein, so if you had bleeding there, yes, it would make it through to the feces.
Stomach ulcers are the better-known ailment at this time, and scoping gives a very good visual diagnosis. Hindgut ulcers have been harder to diagnose, and have been a bit of a catch-all term for people trying to self-diagnose horses that seem NQR.
The causes of ulcers in the stomach and in the hindgut are very different. Typically stress and exercising on an empty stomach for stomach ulcers, and more to do with gut microbe levels in the hindgut.