I've done 4 migrations this way - set up a new version 3 datacenter and export the VMs from 2.2 and import into 3.nn. It works. Mostly. Something messed up my export domain during one migration but I think that was a hardware problem. And it's the only really viable option I could find - the documented procedure to set up a 3.0 datacenter named identically to the 2.2 datacenter will still require you to export/import your VMs eventually.

Note that the export/import strategy needs enough storage to handle both copies of all your virtual disks while migrating. But the end result when you're finished will be worth the cost.