I've only shot one wedding at the Aventura Spa Resort. Im not sure if they have changed their resort policy yet, but we were told they did not allow any outside vendors but allowed us on the one time.
I have gone on a rented catamaran with a small group for the wedding. You have to remember that this will take up a fair chunk of time to get everybody organized, transported to the boat, tour and back again... so this may be something to think about.
While this is a great idea to gather everybody for an adventure... my only suggestion would be to organize it on a different day than your wedding. Take your wedding day in as it unfolds and enjoy every minute of it. Don't try and do too much. There is already enough going on that you need some time to even relax... especially on your wedding day. Even if its for 20 minutes. Everybody always loves the cocktail hour! That is my only advice.
Here is a link to the Aventura Spa Wedding I shot over a year ago: