Be sure it's not white sand grains stuck to his slime coat. If it ever moves, it was not ich.
Yes, they can get it if their slime coat is damaged. Some people 'dip' new fish, and it's a bad idea to do it with a mandy for exactly that reason. Usually if they do get it, it's a case of really unfriendly water quality, damaging the slime coat, or a sickly fish, possibly one starving.