a lot will be determined by the dsize of the shrimp and the size of the discus and the ammount of cover available. Its a managed risk situion eithor way.
larger - non bite size shrimp like the flower shrimp (bamboo) will stand a much better chance with adult discus vs cherry shrimp. It will also depend on how well fed your discus are
It will also be an animal to animal basis.... i've seen some discus actively hunt cherry and amano shrimp and others completly ignore them!