If I'm wanting to make a vanilla cake with cookies and cream filling, what icing should i decorate with? I normally use buttercream dream, is that good?

I think it would be good. I think BC goes with everything!

Is the cookies and cream recipe better than just mixing oreo's into the bc icing?

Since the cookies and cream filling requires refrigeration, I'd opt for the following frosting.

Whipped Cream Frosting:

http://www.cakecentral.com/cake_recipe-901-Whipped-Cream-Frosting.html

This is also very good:

http://www.cakecentral.com/cake_recipe-2110-Marshmallow-Creme-Buttercream.html

HTH