If you have a tank with inert substrate (i.e. sand or gravel), then you *DO* want KH to help keep the pH stable. This may be even more important if you might be using anything that could cause pH swings - i.e. CO2.
HOWEVER, tanks with buffering substrates (i.e. substrates meant to lower pH) use acids instead to keep the pH stable and low. Adding KH into these tanks can cause unstable parameters as the substrate absorbs KH and releases acids (tannic, humic, fulvic...)
When it comes to Neocaridina, stability is recommended over chasing "ideal" parameters... unless of course the shrimp simply aren't thriving for a specific reason... i.e. GH too low, temps too high, etc.
When it comes to Caridina species... now, that'll depend on your Caridina... they could live in extremely soft water (0-3 KH, 0-3 GH) to extremely hard water. (saltwater...) Some might live in both! Depending on life stage of the shrimp. (i.e. amanos, bamboo shrimp, and?) Certain "strains" (not species, but 'type') may live "okay" in high pH water but there will be limited to no breeding and/or offspring survival unless the pH is low.
In short, there's a lot of variables!