Q1P1: Yes we have overseen, and/or gave support to, many imports from a large variety of source systems and versions.
Q1P2: Trigynowhat?

(and the lack of this knowledge never stopped me from performing a migration)
Most of your current questions i can not give a good answer to:
- 90% of the customers who use our importer, never contact Support (guestimate). We do not have knowledge on how they are using our import script or from which source systems/version they come from.
- Even for those who do contact support, we do not keep any numbers on the amount of imports performed or for which systems.
I suggest that you read/post on the ImpEx forum at
www.vbulletin.com. You will very likely find threads from other customers who performed a DCF import in the past or you can post to ask for experiences with this.