When Christain said this is all real, everything that happened was real it begs the question what level of real are we talking about. Christain as we see him is dead yet calls himself real thus the island and the events of six seasons are as real as him.
I think the island is real in as much as the characters we see were there, but they all had the on motives as to what they believed the island could do for them in their death/denial state, some may call a limbo state. A few character examples are:
Before/on death
Lapidus always felt guilty about not piloting the original Oceanic 815.
Miles thought he was born on the island and wanted to know why his father left him - In his flashback his mother told him his father throw them out, she made no mention of the Island - but he lands on the island and is looking for his father and is able to establish a relationship by going back in time.
Charlotte claimed she had lived on the island, in her flashback her mother told her she had made the island story up. Maybe in her death she resolved to find the island again which when she did moved on with the parting words this island is death.
Rose wanted to be cured of cancer and to live happily with Bernard. They were able to achieve this when the island moved time and the made their camp up out of prying eyes.
Micheal had missed out on Walt's upbringing and felt guilty about not being there. His stories with Walt were about fighting to get Walt back, unlike what he had done in his flashback where he allowed Walt to be adopted with not much of a fight, and prove he was worthy of Walt's love.
In Across The Sea, "mother" says to Claudia she got there by "like you by accident", this is disregard of responsiblity for the consequence of an action and a belief that the outcome was not really their intended purpose - pretty much denial.