Joined: May. 99
If you're speaking about the confectioners' sugar in the crust, it's only 1/4 cup, but yes you can use caster sugar if desired. The rest of the sugar in the recipe calls for granulated sugar and that is basically the same as caster sugar, although caster sugar is a bit finer. One can be substituted for the other.
Hope you make the cheesecake and please if you do, let me know how it turned out.