Weddingbee boards

Just like most brides, as a photographer I carry an emergency kit on me whenever I shoot.  My rainy day gear contains towels (to dry an area off before anyone sits on it), a big umbrella (to stay dry of course and also for the cute in-the-rain shot), and chalk, baby wipes, and a Tide pen (just in case someone does get dirty).  It would be worth it to mention your concern to your photographer, and ask him/her to be prepared.

Also, if it does rain, DON'T let anyone rush you out the door until you're ready!  When you need to walk outdoors, take all the time you need to get ready - and get all the help you need from your bridesmaids!  I've seen many brides get the train and skirt of their dress wet and muddy because they allowed themselves to be rushed and didn't take it slow or wait for help with their train.

Tallbride is right about the light - overcast days are the best for shooting outdoors, because the light tends to be soft and diffused, and it makes colors just pop beautifully.

You can get a great rain shot without exposing yourself to the elements if your venue has any type of porch or entrance with an overhang.  You and your guy can stand there, out of the rain, and your photog can go out in the rain.  It'll look great and you get to stay dry!

Hope this helps!  Good luck!