The DbUnit framework is actively developed and tested with OracleDatabase and HypersonicSQL. DbUnit uses a fairly simple SQL syntax and is compatible, out of the box, with most of the others relational database systems. From time to time, I also do testing against MsSQL and MySQL databases. — ManuelLaflamme
Here is a list of relational databases people are using with DbUnit. Feel free to add missing ones and to leave feedbacks about your experience with DbUnit and your RDBMS. Don't forget to increment the usage counter for RDBMS you are using!