i think if the horse has lots of feather or a thick coat, hosing without drying can make them have wet legs for longer which could make mud fever more likely
if the legs are clipped or fine coated, hosing them off should be ok as they will dry pretty quickly
i wash their feet but not their legs unless they are covered in wet mud.(all got fairly fine coats)
I do if he's gonna be ridden the next day, because he wears boots. I usually wash his feet because he wears over-reach boots in the field and they can rub if put on over muddy feet. Some days I just wipe it off with straw and brush in the morning. Today I scrubbed with hibbiscrub because they feel a bit rough so I think he has a little bit of mud fever. Tomorrow will plaster in baby oil before turnout
No, have never hosed the mud off. I let the mud dry overnight then only brush it off lightly if I'm riding but I leave it if he's just going out in the field again.
Jerry had mud-fever when I first had him on trial but has not suffered with it all since I have owned him.