I'm not very familiar with crabs, but aren't red-claws a brackish water crab? while Ghost Shrimp are a freshwater species... so i think your going to have possible problems there?
Also, as mentioned above, the crabs do need a land area to essentially dry off as well... so you may want to keep that in mind... As for Size, i Ghost Shrimp normally i don't think exceed 2" max, and yes, i'm going to say there is a good chance the crabs will kill your shrimp...
I used to have marble crays kill ghost shrimp and freshwater prawns all the time... so i'm sure the crabs will also be more than capable of killing off the shrimp if given the chance...