I can confirm that ,I just did a huge import.
The importer does not care if there is a duplicate forum name.
It just will add another row in the database with a a new forum number.
Same goes for categories.
It will add the same name so besides merging members you also will be charged with the task of moving posts and then the issue with PM's Since those members numbers will be duplicated if there are identical members.
As I can see the current member base you have is less than 100.
So it make take a while but not excessive.
I have no idea how many posts/members,pm's you have in your archive forum.
But as Gizmo stated already.
I would create a test forum and do a dry run first.
Even if it is a success I would make a complete backup of the database and files before doing an actual conversion.on the live board.
