It depends on the type of Caridina you want and what parameters they were potentially raised in.
If we're talking tigers, then the majority of them will be fine on sand with RO water and GH/KH minerals.
If we're talking low end crystals, potentially the same.
However, if we're talking about mischlings, tibees, high end crystals, taitibees, etc.... then yes, you want an active substrate that lowers the pH of the water and keeps it stable with the use of tannins released from the substrate. Many of these shrimp might live, but not thrive, at higher pH levels. There may be minimal to no breeding at higher pH. If there are any offspring, they might not survive to adult-hood.