1st question - Not really. It should not since salt crystals do not have solvent content as high as protein crystals.... Therefore, izit will not be able to go inside salt crystals. its possible that the buffer used for crystallisation might result in izit dye getting precipitated around the salt crystals and therefore, might lead to misinterpretations.

2nd question- Yes, it is possible, depending on the solvent content again.

Many other ways to distinguish between salt and protein crystal are available, like trial by fire, dehydration, birefringence test etc etc

Best