Why would you need to use it? Goats should not have a recurring problem with footrot, they will usually avoid being in wet areas of a field and not be outside in rain etc. Individual incidences (most likely actually during winter when inside on deep-bedding) should be eradicated with regular footbathing, correct trimming and if necessary AB's. Then cleaning out the bedding and using a stable sanitizer there should be no recurrence.
I have not heard of any goatkeeper vaccinating their herd with footvax. Given that goats seem to have more incidences of adverse reactions to vaccines I would not try it to be honest.