I"m completely blanking but no I have not tested the tap water. I know I need to dechlorinate it.In that case, yes, crabs would be cool. Have you tested the parameters of your tap water yet?
I really recommend doing that so you can figure out what kind of fish or inverts will thrive in your water. I would love to keep some species of fish that require very acidic water and I just can't bc I have liquid rock from the tap. I can't be bothered to install an RO system and all of that jazz.