I really don't know for sure, but I did look at the two most recent upgrades, the 3.21 and the 3.2 files, and there are a lot more files in the 3.2 upgrade zip file.
So it looks like there are changes to the files in the 3.2 upgrade that are not also present in the 3.21, but I assume would be needed.
I am not positive it will work, but I recommend that you get the upgrades for 3.21, 3.2, and 3.1, then drop the 3.21 files into the 3.2 upgrade folder, then those files into the 3.1 folder. That should overwrite the older version files with the newer ones, and give you a folder with a 'composite upgrade' from 3.0 to 3.21.
It may be better just to upgrade one version at a time though if any problems occur, that way you can search for issues regarding that specific version upgrade and know exactly where the installation broke down.