hoof oil vs water-based products and frying hooves

Now that the heat has come, my mare's hooves have become very dry and the annual angst about the best hoof products for her has begun. When I was young we used hoof oil and that was that, all year round, but mainly just for competitions. But that was in the UK, ie always damp! Now I have re-started my horse-life after a 20-year break, and here in France, and when I research UK sites, nobody seems to use hoof oil or grease any more, on the basis that it prevents water being absorbed by the hoof and makes it effectively impenetrable. So last year I started using NAF hoof moist but found it didn't go very far. I used aqueous cream too, as a cheaper version but that wasn't very effective either. I have been using REVIVET for cracked hooves as we had some shoeing problems and that was great, until the temperature rose. Now I have bought a huge tub of hoof moist because my pot of green hoof grease has disappeared from the tack room. It seems to be ok with my new mare but you do need to use it a lot. Finally, a weird question has been nagging my brain - if you cover the hoof in oil or grease in hot sunshine, will the hoof wall effectively fry? And if not, why not?