I've recently done an upgrade from 5.1 to 5.2 on Linux and Windows installs of OnCommand Unified Mgr (DFM).
It's very easy. Both the Linux install shell script and the Windows installer will prompt you whether you want to do a fresh install, or an upgrade.
We had no issues with the DB upgrade, but you should still do a DB backup prior to the upgrade as best practice.
I hope this response has been helpful to you.
At your service,
Eugene E. Kashpureff
Senior Netapp Instructor, Unitek Education