This week's book giveaway is in the OCAJP forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide 1Z0-808 and have Jeanne Boyarsky & Scott Selikoff on-line! See this thread for details.
I know that one of the DB's they test with is Derby, which is similar to DB2 but I don't know if there are any issues with ddl gen on DB2 specifically. You might get a better response on the Glassfish forum. You can talk to the developers, there, and see if there is any existing known issue in the issue tracker.