I know I'm late to the party, but this is the approach I took to using SASS in a Java project with an Ant build:
http://workingonthecoolstuff.blogspot.com/2011/02/using-sass-in-ant-build.html To summarize, I'm doing the build on a machine with Ruby and Sass installed so it was as easy as calling the sass command/application using the Ant "apply" task with a fileset that includes all the SCSS/SASS files.
