yes u can put red cherry shrimp and crystal shrimps together. Right now i have around 30 red crystal in my 10gal and with alot of red cherry shrimp and its hard to keep the crystal alive becz of the ammonia and the water quality has to b right just for the red crystal to stay alive.
u have to remember some shrimps die faster from ammonia and water quality. thats the reason why everyone starts out red cherry shrimps becz they are easy and can handle almost anything.