Hum, where did you hear that? =)
Gobys can get ich. I believe all fish can get ich, its a parasite however some fish with denser slim coats (like mandarins) are less likly to get ich as the parasite has a harder time attaching.
But immue, would mean that a fish could not get it and if you do a search I am sure there are pics of gobies with ich.
(in fact, last weekend when I was at my LFS there was a sleeper goby, a small juvi with ich).