I know this is a very old topic but in case anyone else needs to do this, I have done it successfully. I ended up finding and modifying snitz2phpbb2convertor-1.7 scripts to migrate my Snitz DB to Dragonfly.
The scripts are written with the assumption that your Snitz DB is on MySQL. Mine was Access so I first had to use the new MySQL GUI tools which have an awesome migration tool to import from Access to MySQL.
Server specs (Server OS / Apache / MySQL / PHP / DragonflyCMS):