When I cover a cake with cream cheese frosting in fondant, I put cream cheese frosting between the cake layers, and frost the outside in white chocolate ganache to make a nice hard shell for the fondant. 12 ounces white chocolate and 4 ounces heavy cream will frost the outside of an 8 inch by 4 inch tall tier. Swiss meringue buttercream with cream cheese stays a bit too soft at cold temperatures, so it's not ideal for fondant. I have used it in a thin coating under fondant before,though, and it was ok. I just did a red velvet cake yesterday, 8-inch, baked in 3 layers, split into 6, and filled with cream cheese SMB (I made many layers for maximum cream cheese frosting to cake ratio, since that's really why people eat red velvet - for the frosting!) Then I did the upside down frosting method to frost the outside in white chocolate ganache, let it set up, and then covered it in fondant. Nice and smooth, super sharp top edge, as requested by the customer.