Desires is more like a lounge but it's nice enough, I actually saw a couple of after parties when we were there...even though it won't be private I'm sure they can let you decorate a bit, at least the tables if you want. They have good music and stays open until 1:30. Someone else mentioned Mandala, it's the newest nightclub in Cabo, great ambiance. Maybe you could reserve tables for some of your guests.
I tried making reservations at any of the Dreams restaurants for our rehearsal dinner but they are very strict with their no reservations policy. It would be around 20 of us so I cannot just show up hoping they will sit us together..they can't guarantee it. I still don't know what Im doing for my rehearsal or my welcome dinner. Im thinking of a tequila tasting, El patio, I have to speak to Yesica to see how that goes...