It's clearly not clairvoyance, but memory. The disappointment, especially felt by Charlotte for Dan, seemed to be related to a prior condition, rather than some clairvoyance skill the wasn't working on the island as they had expected. Dan definitely displays many of the affects of someone who is autistic: social skills not up to speed, odd tics, but intense focus & ability in certain areas. They were clearly hoping for some healing. Which makes sense, since they obviously know about many of the island's properties already.
So, the question is, why could Locke walk immediately upon arriving on the island, while Daniel apparently hasn't healed?