I heard the rule of thumb for most shrimp is 2 inches of shrimp per one gallon of water, but if you do water changes (or in the case of a one gallon setup, "mini" water changes) there's no reason you couldn't keep up to 4 or 5 cherrys or even up to 6 ghost shrimp.
You could look into amanos but GOOD LUCK with them, especially in a small tank.
Personally, I wouldn't put anything in a one gallon set up that I wasn't purposely trying to torture. Maybe a snail...
I used to keep a betta at my desk at work in a gallon bowl, but I changed the water and cleaned the bowl twice a week until I quit that job and brought the betta home to a bigger bowl (and still have to clean it twice a week, damned crapmachine!)
I would say one gallon is too small for a wood shrimp.