The vBulletin importer isn't finished yet, but should be finished shortly. As for a FusionBB importer, you might have to wait until UBB.threads version 7.4.
If you are in real need, any import from any product is possible. If there's no importer available, it basicly says there is no 99% fullproof generic solution available.
If you want to to have a conversion, I know of people for hire. It would just be more costly since it would involve a lot of manual labor, depending on what data you want to import.