I've never been to Dreams, but I have a feeling that weddings at the Riu Palace probably have to shut down at 10:30 as well. Most places in Cabo have that rule.
You could always stay at the Riu Palace and have your wedding at a non-resort location, like a restaurant such as Sunset Da Mona Lisa or something? That would probably be much pricier though.
There are a TON of Dreams brides on here so you can be assured that it's a beautiful resort and that the weddings there are amazing!