Can I use white chocolate cream cheese frosting to make a ruffle cake or will it be too soft?
Never done this technique.
It depends on how you want the ruffles:) Are you making a completely ruffled cake?
W/o a picture of what you are trying to do it's hard to know for sure.
If you want the upper part of the ruffle to stand away slightly from the cake, yes it should be possible. Use top 104 to pipe a slight aigazg motion around the cake. Start at the top & work down, just slightly overlapping the previous one.
If you find the icing is too soft, add a bit more powder sugar mixed w/a tablespoon or so of cornstarch.
I would like to do the vertical ruffles on the whole cake.