I am working on an assignment (big smokes) which entails a similar concept, abstracting a web service behind a DAO is a good idea..because by definition a DAO is a data access object and data could be accessed from anywhere (Mainframe, Web Service, Database).
I have used this pattern in real life projects and it works really well...not when it comes to sun exam..not so sure
OCMJEA/SCEA, SCDJWS, SCBCD 1.3, SCJP 1.4
My SCEA experience:http://javalogue.blogspot.com/