I think you are asking if DB2 can commit updates that were performed in a single UOW, which the answer would be no. If you issue an update against a billion row table, there is nothing to commit until all billion rows have been updated, as you have a single update statement running.
You will want to look into performing the updates in pieces/parts. Maybe you could load the data into another version of the table, with the update being what you selected from the orginal table, then rename the new version and drop the old. If you search through the forum here there have been past discussions on those types of topics.