A lead rifled slug is no more apt to damage the rifling than biting into a plastic sabot.

The leading will be worse, so you'll need to clean frequently. If you recover slugs and see any smearing, then you know you're not getting proper base obturation of the slug.

I'd personally say - based on experience as well as the physics behind it - that a rifled slug in a rifled barrel makes a he11 of a lot more sense than a smooth bore barrel with a rifled choke!!!!