I would be leery of trying to self-treat a sarcoid with a cold treatment. Sarcoids are particularly nasty because any irritation (including attempts at treatment) can lead to them growing aggressively. Each attempt at treatment that fails also decreases the likelihood of future treatments succeeding. So, treatments should be chosen and applied carefully.
I have never heard of using Dr. Scholl's on sarcoids so add that to the two facts I listed above, I would be concerned about actually trying this. .
Is the vet who recommended this an equine vet? If not, discuss this with an equine vet to be sure you are making the best choice possible for your horse.
Licensed Veterinary Technician