As long as the data is amenable. There are certain things in our system that defy easy testing because of the setup involved.
CRUD stuff is fairly easy to test. Use one data manager method to create the test data and another to remove it. I usually make the data include something that designates it as a unit test record, eg. prepending user names with "utest_". Then in the tear down test method I run a delete where user_id like 'utest_%'.
I usually build the data manager classes first, with unit tests. Then I build a mock data manager to the same interface. As a result, when I get to the controller and JSP portions I don't have to worry about data issues.