yes, I have red cherry shrimp in a 2 gallon fish bowl and also in a 1 gallon "pickle jar" with no substrate. just moss. In both cases, they do well and have even bred. I notice they are not nearly as colorful as the shrimp in my other tanks that do have substrate (fluorite in one and black gravel in others). A 30 gallon tank with no substrate may look kinda barren. The gravel gives more surface area for biofilm to grow on. You could also add leaf litter.
the cherries will generally color up with a dark substrate and have less of an intense coloring in lighter substrates. So I have no idea how java moss will affect their coloring but health wise I think they will be fine
so 4 months ago i decided to go with black eco-complete, some rock, driftwood, java moss and assorted plants.
i bought 25 red cherry shrimps from one of the hobbyists on this site. about 10 of the original shrimps have died but the rest have started a small colony in my 30G. today i have about 100 of these little guys inside the tank.