I guess being high in saponins would come in handy! Less likely for the hermit crabs to come to the conclusion to eat it!

Mondo grass (as I use to calling them

) are sold in freshwater aqua like you mentioned, so it could conclude that it's safe and doesn't "leach" anything into the water column. That means that the plant should be ok with crabs, as long as they don't get their claws on it. Not to mention, frog keepers have used them in their terrariums without apparent problems.
So I would say a hesitant yes. After all, a lot of the plants crabbers have tried out with their crabs aren't exactly safe (pothos for example) and the hermies seem to do ok.