HI there Mark.
I have a discus tank and i have in it two big shrimps. The are more like small lobsters, but without any pinchers so cannot catch fish. They are called either mountain shrimp or rock Shrimp. They are docile and do not cause any trouble, in fact i have small tetras in it and do not worry them. The only thing is that they lead a very secretive life, and I have only seen them a couple of times since I have put them in the tank. So I know they are there but nothing else. They are quite big in size around i would say 5cm if not more,so they will certainly will not be eaten by the discus. Having said that, if there is pleny of hiding space especially plants the amano shrimps wll survive. I do not have any yet, but I have seen a friend's planted tank and he had plenty of them in it.
Hope this helps you a bit
Frank