AI'm suppose to be making a pregnant belly cake and they want red velvet and cream cheese filling. I have a wonderful cream cheese filling but the belly of the cake is going to be piped roses all over. Should I use cream cheese frosting? Or regular buttercream? I don't think the filling/frosting I have is crusting and I want my roses to hold up. I don't really have time to experiment. Please give me some advice!

Here are a couple recipes with lots of comments you should be able to get an idea how it worked for others:

http://www.cakecentral.com/b/recipe/wedding-crusting-cream-cheese-frosting

http://www.cakecentral.com/b/recipe/crusting-cream-cheese-icing

I would do a test first, but when in doubt stick with the BC you know will work.

For cream cheese frosting, I usually just sub some of the butter in my usual quick, go-to buttercream for cream cheese and it holds up and pipes just as well.
 

Where I normally use 3 sticks of softened butter, I instead use 2 sticks and replace the third with 8oz softened cream cheese.

Mix the butter and cream cheese with about 7 cups of powdered sugar until it's really creamy.  Then add about a tablespoon of heavy whipping cream (or more for consistency preference) and a teaspoon of vanilla extract and mix it for another couple minutes.