It should still work, I've heard stories of people washing them and the card working fine (My teacher did it for fun on an old card to test it).

Personally, for something like this (sounds like a paid gig?) CF cards are cheap enough, I'd pick up one or two more for the event, then take the washed one out a different day and go shooting with it to make sure it works fine.

If the card decides to fail on you, better shooting your own stuff than someone elses.

Good luck though!