MediaWiki 1.15 was released with partial DB2 support, but unfortunately there were some changes to the database schema that I missed and it didn’t work out of the box. Since then, I’ve committed several fixes to the main development trunk. The trunk is currently destined to become 1.16alpha, though theoretically I could backport these to the 1.15 branch.
My Apache is currently crashing willy-nilly on startup. Hopefully, there are no silly development bugs left in.:-)