If it is safe for horses it should be safe for goats too, contacting the manufacturer will not get you any answers, because it will not have been tested on goats (too expensive and too small a market). You could also ask your vet - he may have had similar enquiries from dog/sheep owners. What is used on cattle?
Fortunately we do not have midges dring the day, but as we are next to the river in the evening they do come out in force... our goats are not out in the evening.