Regarding Tori's memory loss, traumatic events have been known to cause the brain to shutdown short term memory as a coping mechanism. You see it more in victims of conflict or as part of PTSD. Usually the lost memories will come back on their own or through talking through the events.
As for the models looking so good after some time on sea, are they though? Olga looks like she's healing from sunburns, Jenny (okay, not a model) seems on the verge of freaking out being any body of water deeper than a pool. But seriously, look up people who have been lost at sea or in survival situations, the human body can do a lot of crazy shit to keep itself going.
And the idea that its all an elaborately staged stunt for a survival, yeah, I can't see it. Its one of those scenarios where, sure, the initial set-up might work (the storm, the wreck, the mysterious resort), but after that, they are too many variables that make the whole thing dangerous, even for reality tv.