It does support UBB5 (as well as 6), but you'll need shell access to run it. You might be able to run it using FileMan. If you load up FileMan, go into the tools directory, then click on the 'Command' link in the top menu, you'll be able to enter a command in the text input at the bottom.
If you input just:
./import.pl
you'll get the instructions on how to use it.
When you actually run the import, you'll want to use the 'Long Running' option.

Adrian