Welcome to Barnmice Tami!

Though I had one horse with a big blaze it was nowhere as big as you guy's.

At one barn I saw them use zinc oxide ointment on the muzzle but I do not know how safe this would be around the eyes.

You could try a fly mask and regularly put sun screen on the fly mask.  Just make sure to check under the fly mask daily in case anything gets in it.

I do not know any tips for growing out mane hair.  Maybe you could collect main and tail hair from horses and braid it in, sort of a hair externsion thing. 

Bless you for working with this horse, and you said he was deaf?  What a challenge that must be.

I never had to work with a deaf horse.  The type of training I used to do with my horses started off with voice commands, lol.  It sort of boggles my mind trying to think of training a horse that cannot hear "good boy." 

I can't do this (I've tried) but some horsemen communicate with their horses through mind pictures.   

Have you ever considered learning ASL?  The longer I've been around horses the more I believe that some of them actually learn to understand English.  Since ASL is a little more in line with how horses communicate than spoken English your horse might enjoy learning it, maybe you could combine a clear mind picture with the sign.

Also I've read that horses "hear" through their hooves, and this is why they know storms are coming.

I admire you greatly for working with the deaf horses, it must present you with unique challenges that the rest of us horsepeople never run into.