i never restored 9.3.1 UCS to 10.2.2 but i have done 9.4.x UCS to 10.2.x and it was fine except license which i had to re-activate and a few configuration which is not compatible in 10.2.x. anyway, it was not a big deal.
the other way is to export 9.3.1 to SCF and import it to 10.2.2. this is simpler but SCF does not contain all files e.g. certificate/private key. so, you have to manually import them.
sol8435: Overview of the single configuration file (SCF)
Mostly straightforward... There might be a few parts of the config that dont load though. Best advice is to grab a test unit and update to 10.2.2 and import the config ahead of time so you can see what needs to be fixed up by hand.