I'm thinking Desmond IS NOT one of the 'others' I think the others are roughing it on the island, just like our castaways. BUT, Desmond may not be alone in the 'bunker'. He was sleeping in the top bunk....did anyone notice the condition of the bottom bunk?
Lots of bunker questions, electricity/fresh food/major weapons stash/etc.
I did think it a bit farfetched that Jack recognized Desmond so quickly. Do you think you'd recall the face of someone you spent just a few minutes with over five years ago ESPECIALLY under the stressful circumstances? Of course, we don't know if Jack has seen Desmond SINCE the stadium encounter