I've had Appaloosas for a little over 30 years. I've had one go blind at the age of 22.
According to my experience...and the vets I've talked to...the horses with pink eye rims are at the most risk. Appaloosas, and some other breeds, can have pink (non-pigmented) eye rims. Apploosas also tend to have fine, often sparse hair that may result in thin eyelashes that cannot protect the eyes very well.
So, yes, the incidence of blindness may be higher in Appaloosas than in some other breeds.
If your horse has dark, or mostly dark, eye rims, then the risk of blindness is no different than any other horse with dark eye rims.
If your horse has pink eye rims, you'll just have to be careful to keep close watch for redness and irritation. If your horse won't wear a fly mask (the mare I had who went blind would scrape her face raw to get a fly mask off so I gave up on them) during fly season, you need to take extra care to keep fly repellent on the face and around her eyes and medicate the eyes at the first sign of irritation. Bright sunlight often irritates pink-rimmed eyes, too.
Word of warning: Be sure to work with your vet on eye medication. Ulcers and conjunctivitis can look the same in the early stages but using conjunctivitis medication on an ulcer or vice versa and you could have a total disaster.