I would say not. Compare the exoskeleton of a Centruroides which is exposed to some sunlight to an obligate burrower such as Anuroctonus and you will find the reverse of what you have suggested.Is a scorps shell harder if it comes out more?
The truly squishy scorpions seem to fall more along the lines of species that wedge themselves into tight cracks than by sun exposure. Hadogenes would be an example of a squishy arid scorpion whereas Opisthacanthus would be an example of a squishy scorpion found in wetter climes.Are dessert scorps shell harder than forest scorps.
Those would be primarily urates. Animals that aren't so hung up over moisture loss (us) tend to put out urine. Those that retain a lot of moisture tend to put out a much dryer compound of one type or another, usually appearing chalky and white. If you start putting out solid calcium then you're in trouble.Is this why there feaces are powdery and white