I think one should be okay. Maybe I am saying that because I have a lone Wood shrimp in my tank. Even at the LFS where they had several in a tank, they all seemed to hang out on their own, they didn't seem social to me. I am only guessing, but I'd think cherry shrimp would be similar or the same.
The only "issue" with keeping my shrimp by himself is that I rarely see him unless I look really hard.He mostly is active at night when the lights are off. I've tried observing him with a flashlight, but he hides from that too, so now I just leave him alone to do his thing.
\Dan