I want to make a carrot cake for my wedding cake. Will cream cheese frosting work to decororate on??

Like buttercream??

The cream cheese frosting I make, which is a typical classic recipe,  is way too unruly to cooperate for normal decorating, so I use it as a filling and then ice the out side with buttercream.

Also, not all carrot cake recipes hold up well with a lot of weight on them - you might want to do a test run just to maje sure it's not going to crumble. (like a 4 layer, 8 in round)

I use the white chocolate cream cheese buttercream from The Cake Bible.

It is only slightly thicker than IMBC and I have made wedding cakes with it. 

I use Decorator's Cream Cheese frosting.  It's a crusting cream cheese frosting that's great for decorating on.  You should be able to find it here under recipes. 

I worked in a bakery that only used the white choc cream cheese frosting from The Cake Bible.  There is a learning curve to it.  It took me a while to be able to get it smooth and look good on a wedding cake.  I personally think it's gross (just made and smelled too much of it), but you can get it smooth like buttercream.