Yogi:
Here is the fact-sheet on the Dixie 'Terminator' slug, they definitely specify rifled barrels, and there are no 'rifled ribs' on the slug of any sort:

Dixie 'Terminator' Slug

Here is a pic of the Dixie 'Predator' slug, also no rifled ribs.

I had assumed you know that rifled ribs on a shotgun slug do NOT impart any spin to the slug, neither within the barrel nor in the air during flight. They are simply a collapsible centering device to keep the slug straight as it passes through varying degrees of choke in the various shotguns in which it will be fired. Successful slugs need some way of achieving stability, and maintaining it in flight. The 'moulded fins' you refer to may well achieve this, but a Dixie slug won't unless fired in a rifled barrel.

Anyway, give them a shot by all means, you just never know till you have a go!