I can see it but I how would they find out? Desmond, Hurley, Charlie & Claire are the only ones who know he can do it... I don't see them blabing it around they don't gossip about important stuff let alone Desmond.. I think Locke thinks something is going on with him but nothing about flashes and such... JMHO

__________________
Please don't give up, Des. Because all we really need to survive is one person who truly loves us. And you have her. I will wait for
you. Always. I love you, Pen

DESMOND: I love you, Penny. I've always loved you. I'm so sorry. I love you!
PENNY: I love you too.
DESMOND: I don't know where I am, but--
PENNY: I'll find you, Des--
DESMOND: --I promise--
PENNY: --no matter what--
DESMOND: --I'll come back to you--
PENNY: --I won't give up--
BOTH: I promise. I love you.